Re: [PATCH v2] kbuild: Add inline-account tool

[Masahiro Yamada]

On Wed, Nov 15, 2023 at 9:49 AM Andi Kleen <ak@xxxxxxxxxxxxxxx> wrote:


This is a standalone script, which is unrelated to kbuild.

Please change the subject to

"scripts: Add inline-account tool"





>
> A common cause of binary code bloat is excessive inlining. Traditional
> tools (like nm --size-sort -t d) don't address that directly because
> they only see the final functions, but don't know about inlines.
>
> This patch adds inline-account that makes it easy to track that down
> by accounting code bytes to all functions visible in the debug information,
> as well as code lines.
>
> Here are some examples:
>
> Show all inlines that increase code size by >1K in the core scheduler:
>
> $ inline-account.py --min-bytes=1000 kernel/sched/core.o
> Total code bytes seen 75690
>
> Code bytes by functions:
> Function                                           Total          Avg   Num
> rq_pin_lock                                        1401  (0.02%)  35    39
> __sched_setscheduler                               1277  (0.02%)  41    31
> perf_fetch_caller_regs                             1012  (0.01%)  17    58
>
> Code bytes by nearby source line blocks:
> prefix /home/ak/lsrc/git/linux/
> Line                                               Total
> kernel/sched/sched.h:1610                          1387  (0.02%)
> include/trace/events/sched.h:16                    1172  (0.02%)
> include/trace/events/sched.h:222                   1058  (0.01%)
>
> This indicates that rq_pin_lock should likely be not inline,
> and perhaps perf_fetch_caller_regs not either.
>
> Note that not all large inlines are necessary bloat. If there is only


necessarily bloat?









> a single call site it isn't bloat (the tool currently cannot distinguish
> that case). For example it is commonly seen with syscall definitions
> that use single large inlines with only a single caller. In the example
> above I think it's the case with __sched_setscheduler.
>
> Show the >1K inlines in lib/maple_tree.o, which for some reason
> comes in at a incredible 73k of code size:
>
> $ inline-account.py --min-bytes 1000 lib/maple_tree.o
> Total code bytes seen 73578
>
> Code bytes by functions:
> Function                                           Total          Avg   Num
> mas_mab_cp                                         5537  (0.08%)  37    149
> mas_pop_node                                       3798  (0.05%)  28    131
> ma_slots                                           2368  (0.03%)  14    162
> ma_pivots                                          2353  (0.03%)  10    222
> mas_destroy_rebalance                              2056  (0.03%)  42    48
> mas_start                                          1661  (0.02%)  13    125
> mas_set_parent                                     1454  (0.02%)  20    72
> mas_set_alloc_req                                  1410  (0.02%)  17    80
> mte_node_type                                      1360  (0.02%)  5     228
> mas_data_end                                       1189  (0.02%)  16    74
> mte_to_node                                        1085  (0.01%)  3     276
> mas_split                                          1053  (0.01%)  65    16
> mas_topiary_replace                                1033  (0.01%)  38    27
> mas_root_expand                                    1001  (0.01%)  35    28
>
> Code bytes by nearby source line blocks:
> prefix /home/ak/lsrc/git/linux/
> Line                                               Total
> lib/maple_tree.c:210                               1360  (0.02%)
> include/trace/events/maple_tree.h:80               1283  (0.02%)
> lib/maple_tree.c:649                               1193  (0.02%)
> lib/maple_tree.c:288                               1097  (0.01%)
>
> It's clear there is a lot of potential for shrinking here, as a quick
> experiment shows:
>
> $ size lib/maple_tree.o
>    text    data     bss     dec     hex filename
>   72257    5312       8   77577   12f09 lib/maple_tree.o
> $ sed -i -e s/__always_inline// -e 's/ inline/ /' lib/maple_tree.c
> $ make -s lib/maple_tree.o
> $ size lib/maple_tree.o
>    text    data     bss     dec     hex filename
>   47774    4720       8   52502    cd16 lib/maple_tree.o
>
> 34% reduction just from trusting the compiler. Most of it seems
> to come from abuse of __always_inline. I suppose a large scale
> tree purge of that would give some decent binary size results.
>
> $ inline-account.py --show=5 kernel/workqueue.o
> Total code bytes seen 40403
>
> Code bytes by functions:
> Function                                           Total          Avg   Num
> bitmap_copy                                        1477  (0.04%)  26    56
> show_pwq                                           912   (0.02%)  76    12
> workqueue_init_early                               846   (0.02%)  29    29
> __flush_workqueue                                  753   (0.02%)  31    24
> alloc_and_link_pwqs                                558   (0.01%)  69    8
>
> Code bytes by nearby source line blocks:
> prefix /home/ak/lsrc/git/linux/
> Line                                               Total
> include/linux/bitmap.h:268                         1336  (0.03%)
> include/trace/events/workqueue.h:23                1038  (0.03%)
> include/trace/events/workqueue.h:108               732   (0.02%)
> include/trace/events/workqueue.h:59                694   (0.02%)
> include/trace/events/workqueue.h:82                670   (0.02%)
> $
>
> This is an interesting case because bitmap_copy is just
>
> static inline void bitmap_copy(unsigned long *dst, const unsigned long *src,
>                         unsigned int nbits)
> {
>         unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);
>
>         if (small_const_nbits(nbits))
>                 *dst = *src;
>         else
>                 memcpy(dst, src, len);
> }
>
> memcpy (which is a macro) must sometimes generate a lot of
> code. The small_const_nbits case definitely should be inlined though
> because it's likely even smaller than a call. Would need
> more investigation.
>
> The other large inlines are trace points. Perhaps there is something
> there that could be done to shrink that a bit.
>
> Finally we can do a global accounting (currently with multiple runs):
>
> (ignore the percentage numbers since they are just for the local file)
>
> $ find -name '*.o' | xargs -n1 inline-account.py > a
> $ sort -n -r -k 2 a | head -30
> ZSTD_count                                         81799 (0.19%)  32    2514
> ZSTD_count                                         52233 (0.25%)  33    1544
> kmalloc                                            43324 (0.00%)  12    3334
> pv_queued_spin_unlock                              42027 (0.00%)  9     4580
> constant_test_bit                                  41667 (0.00%)  5     8005
> arch/x86/include/asm/paravirt.h:591                41044 (0.00%)
> arch/x86/include/asm/bitops.h:207                  40153 (0.00%)
> __refcount_add                                     37968 (0.00%)  24    1532
> page_fixed_fake_head                               36368 (0.00%)  19    1832
> include/linux/slab.h:599                           35654 (0.00%)
> arch/x86/include/asm/jump_label.h:27               35156 (0.00%)
> spin_lock                                          32170 (0.00%)  10    3007
> __refcount_sub_and_test                            32068 (0.00%)  17    1842
> include/linux/spinlock.h:351                       31102 (0.00%)
> arch_static_branch                                 30874 (0.00%)  4     7022
> get_current                                        30714 (0.00%)  9     3351
> arch/x86/include/asm/current.h:41                  29912 (0.00%)
> trace_trigger_soft_disabled                        29814 (0.00%)  21    1368
> perf_fetch_caller_regs                             27504 (0.00%)  16    1634
> ZSTD_storeSeq                                      26060 (0.06%)  30    862
> hid_map_usage                                      25582 (0.00%)  88    288
> ZSTD_compressBlock_lazy_generic                    24953 (0.12%)  46    535
> ZSTD_compressBlock_lazy_generic                    24953 (0.06%)  46    535
> paravirt_ret0                                      24152 (0.00%)  24152 1
> spin_unlock_irqrestore                             23253 (0.00%)  10    2281
> include/linux/spinlock.h:406                       22526 (0.00%)
> ZSTD_RowFindBestMatch                              21527 (0.10%)  23    922
> ZSTD_RowFindBestMatch                              21527 (0.05%)  23    922
> __list_add                                         21209 (0.00%)  11    1851
> include/linux/refcount.h:283                       20642 (0.00%)
>
> - So my kernel is spending around ~30K just for getting task_structs in
> current.
> - I'm sure ZSTD is great, but is it >200K in duplicated code worth great?
> - page_fixed_fake_head probably shouldn't be inlined
> - There might be some potential in out lining reference counts
> (although that one might be truly performance critical)
> - There's maybe some potential in shrinking trace point bloat?
>
> ... and more similar insights.
>
> Also of course there can be critical inlines that really need
> to be inline in many sites for best performance. But that's rarely the case
> if they are big because it's unlikely the small call overhead is making
> a significant difference for a large chunk of code.
>
> In any case the tool is useful, so I think it deserves its place
> in scripts/
>
> Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
>
> ---
>
> v2: Address review comments. Change balancing to be address based.
> Add option to set objdump binary.
> ---
>  scripts/inline-account.py | 201 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 201 insertions(+)
>  create mode 100755 scripts/inline-account.py
>
> diff --git a/scripts/inline-account.py b/scripts/inline-account.py
> new file mode 100755
> index 000000000000..c32cb0547172
> --- /dev/null
> +++ b/scripts/inline-account.py
> @@ -0,0 +1,201 @@
> +#!/usr/bin/env python3
> +# account code bytes per source code / functions from objdump -Sl output
> +# useful to find inline bloat
> +#
> +# SPDX-License-Identifier: GPL-2.0-only


Please move this above.

The first line is the shebang.
The second line is SPDX.





> +# Author: Andi Kleen
> +
> +import os
> +import sys
> +import re
> +import argparse
> +import bisect
> +import multiprocessing


Please sort imports alphabetically.



> +from collections import Counter
> +from functools import reduce, partial
> +
> +def get_args():
> +    p = argparse.ArgumentParser(
> +            description="""
> +Account code bytes per source code / functions from objdump.
> +Useful to find inline bloat.
> +
> +The line numbers are the beginning of a block, so the actual code can be later.
> +Line numbers can be a also little off due to objdump bugs
> +also some misaccounting can happen due to inexact gcc debug information.
> +The number output for functions may account a single large function multiple
> +times.  program/object files need to be built with -g.
> +
> +This is somewhat slow due to objdump -S being slow. It helps to have
> +plenty of cores.""")
> +    p.add_argument('--min-bytes', type=int, help='minimum bytes to report', default=100)
> +    p.add_argument('--threads', '-t', type=int, default=multiprocessing.cpu_count(),


Please check that args.threads >= 1.

If not, please show an error message.





> +                   help='Number of objdump processes to run')
> +    p.add_argument('--verbose', '-v', action='store_true', help="Print more")
> +    p.add_argument('--show', type=int, help='Number of results to show')
> +    p.add_argument('--objdump', default="objdump", help="Set objdump binary to run")
> +    p.add_argument('file', help='object file/program as input')
> +    return p.parse_args()
> +
> +def get_syms(fn):
> +    syms = []
> +    pc = None
> +    with os.popen("nm -n --print-size " + fn) as f:
> +        for l in f:
> +            n = l.split()
> +            if len(n) > 2 and n[2].upper() == "T":
> +                pc = int(n[0], 16)
> +                syms.append(pc)
> +                ln = int(n[1], 16)
> +    if not pc:
> +        sys.exit(fn + " has no symbols")


"if not pc" becomes true in two cases:
 - pc is zero
 - pc is None


Only the latter case is "no symbols" because
a symbol address may become zero in relocatable ELF.



if len(syms) == 0:
     ...

will work correctly.

And, "pc = None" is unneeded.








> +    syms.append(pc + ln)
> +    return syms
> +
> +class Account:
> +    def __init__(self):
> +        self.funcbytes = Counter()
> +        self.linebytes = Counter()
> +        self.funccount = Counter()
> +        self.nolinebytes = 0
> +        self.nofuncbytes = 0
> +        self.total = 0
> +
> +    def add(self, b):
> +        self.funcbytes += b.funcbytes
> +        self.linebytes += b.linebytes
> +        self.funccount += b.funccount
> +        self.nolinebytes += b.nolinebytes
> +        self.nofuncbytes += b.nofuncbytes
> +        self.total += b.total
> +        return self
> +


Since this script implements a class,
please follow this blank line rule.


https://peps.python.org/pep-0008/#blank-lines









> +# dont add sys.exit here, causes deadlocks
> +def account_range(args, r):
> +    a = Account()
> +    line = None
> +    func = None
> +    codefunc = None
> +
> +    cmd = ("%s -Sl %s --start-address=%#x --stop-address=%#x" %
> +                (args.objdump, args.file, r[0], r[1]))
> +    if args.verbose:
> +        print(cmd)
> +    with os.popen(cmd) as f:
> +        for l in f:
> +            #      250:       e8 00 00 00 00          callq  255 <proc_skip_spaces+0x5>
> +            m = re.match(r'\s*([0-9a-fA-F]+):\s+(.*)', l)
> +            if m:
> +                bytes = len(re.findall(r'[0-9a-f][0-9a-f] ', m.group(2)))
> +                if not func:
> +                    a.nofuncbytes += bytes
> +                    continue
> +                if not line:
> +                    a.nolinebytes += bytes
> +                    continue
> +                a.total += bytes
> +                a.funcbytes[func] += bytes
> +                a.linebytes[(file, line)] += bytes
> +                codefunc = func
> +                continue
> +
> +            # sysctl_init():
> +            m = re.match(r'([a-zA-Z_][a-zA-Z0-9_]*)\(\):$', l)
> +            if m:
> +                if codefunc and m.group(1) != codefunc:
> +                    a.funccount[codefunc] += 1
> +                    codefunc = None
> +                func = m.group(1)
> +                continue
> +
> +            # /sysctl.c:1666
> +            m = re.match(r'^([^:]+):(\d+)$', l)
> +            if m:
> +                file, line = m.group(1), int(m.group(2))
> +                continue
> +
> +    if codefunc:
> +        a.funccount[codefunc] += 1
> +    return a
> +
> +def get_boundaries(syms, sym_sizes, chunk):
> +    run = 0
> +    boundaries = [syms[0]]
> +    for i, x in enumerate(sym_sizes):
> +        run += x
> +        if run >= chunk:
> +            boundaries.append(syms[i])
> +            run = 0
> +    boundaries.append(syms[-1])
> +    return boundaries
> +
> +
> +def process(args):
> +    # objdump -S is slow, so we parallelize
> +
> +    # split symbol table into chunks for parallelization
> +    # we split on functions boundaries to avoid mis-accounting
> +    syms = get_syms(args.file)
> +    if len(syms) < 2:
> +        print("not enough symbols")
> +        return

This message should go to stderr instead of stdout.


   sys.exit("not enough symbols")









> +    sym_sizes = [syms[x + 1] - syms[x] for x, _ in enumerate(syms[:-1])]
> +    sym_total = sum(sym_sizes)


This is equivalent to

      sym_total = syms[-1] - syms[0]

isn't it?






> +    chunk = max(int(sym_total / args.threads), 1)



Do you know the "//" operator ?


int(sym_total / args.threads)

   should be equivalent to

sym_total // args.threads







> +    boundaries = get_boundaries(syms, sym_sizes, chunk)
> +    ranges = [(boundaries[x], boundaries[x+1]) for x in range(0, len(boundaries) - 1)]




Very tedious code.

And, your get_boundaries() helper uses less threads than args.threads.






How about this to compute the ranges directly?



def get_ranges(syms, threads):

    ranges = []
    prev = syms[0]
    i = 1

    while threads > 0:

        boundary = prev + 1 + (syms[-1] - prev - 1) // threads

        while syms[i] < boundary:
            i += 1

        ranges.append((prev, syms[i]))
        prev = syms[i]
        threads -= 1

        if (prev == syms[-1]):
            break

    return ranges





ranges = get_ranges(syms, args.threads)






> +    assert ranges[0][0] == syms[0]
> +    assert ranges[-1][1] == syms[-1]
> +
> +    # map-reduce
> +    account_func = partial(account_range, args)
> +    if args.threads == 1:
> +        al = list(map(account_func, ranges))
> +    else:
> +        al = multiprocessing.Pool(args.threads).map(account_func, ranges)
> +    a = reduce(lambda a, b: a.add(b), al)
> +
> +    print("Total code bytes seen", a.total)
> +    if args.verbose:
> +        print("Bytes with no function %d (%.2f%%)" % (a.nofuncbytes, 100.0*(float(a.nofuncbytes)/a.total)))
> +        print("Bytes with no lines %d (%.2f%%)" % (a.nolinebytes, 100.0*(float(a.nolinebytes)/a.total)))
> +
> +    def sort_map(m):
> +        return sorted(list(m.keys()), key=lambda x: m[x], reverse=True)
> +
> +    print("\nCode bytes by functions:")
> +    print("%-50s %-5s  %-5s   %-5s %-5s" % ("Function", "Total", "", "Avg", "Num"))
> +    for i, j in enumerate(sort_map(a.funcbytes)):
> +        if a.funcbytes[j] < args.min_bytes:
> +            break
> +        if args.show and i >= args.show:
> +            break
> +        print("%-50s %-5d (%.2f%%)  %-5d %-5d" % (
> +                j,
> +                a.funcbytes[j],
> +                a.funcbytes[j] / float(a.total),
> +                a.funcbytes[j] / a.funccount[j],
> +                a.funccount[j]))
> +
> +    for j in list(a.linebytes.keys()):
> +        if a.linebytes[j] < args.min_bytes:
> +            del a.linebytes[j]
> +
> +    prefix = os.path.commonprefix([x[0] for x in list(a.linebytes.keys())])
> +
> +    print("\nCode bytes by nearby source line blocks:")
> +    print("prefix", prefix)
> +
> +    print("%-50s %-5s" % ("Line", "Total"))
> +    for i, j in enumerate(sort_map(a.linebytes)):
> +        if args.show and i >= args.show:
> +            break
> +        print("%-50s %-5d (%.2f%%)" % (
> +                "%s:%d" % (j[0][len(prefix):], j[1]),
> +                a.linebytes[j],
> +                a.linebytes[j] / float(a.total)))
> +    if len(a.linebytes) == 0:
> +        print("Nothing found. enable CONFIG_DEBUG_INFO / -g?")



I thnik this should be checked much earlier.

If CONFIG_DEBUG_INFO is disabled, there is nothing to print.



> +
> +if __name__ == '__main__':
> +    process(get_args())
> --
> 2.41.0
>


--
Best Regards
Masahiro Yamada