[PATCH v7 00/12] iov_iter: Convert the iterator macros into inline funcs
From: David Howells
Date: Mon Sep 25 2023 - 08:04:08 EST
Hi Jens, Christian,
Could you take these patches into the block tree or the fs tree? The
patches convert the iov_iter iteration macros to be inline functions.
(1) Remove last_offset from iov_iter as it was only used by ITER_PIPE.
(2) Add a __user tag on copy_mc_to_user()'s dst argument on x86 to match
that on powerpc and get rid of a sparse warning.
(3) Convert iter->user_backed to user_backed_iter() in the sound PCM
driver.
(4) Convert iter->user_backed to user_backed_iter() in a couple of
infiniband drivers.
(5) Renumber the type enum so that the ITER_* constants match the order in
iterate_and_advance*().
(6) Since the preceding patch puts UBUF and IOVEC at 0 and 1, change
user_backed_iter() to just use the type value and get rid of the extra
flag.
(7) Convert the iov_iter iteration macros to always-inline functions to
make the code easier to follow. It uses function pointers, but they
get optimised away. The priv2 argument likewise gets optimised away
if unused.
The functions are placed into a header file so that bespoke iterators
can be created elsewhere. For instance, rbd has an optimisation that
requires it to scan to the buffer it is given to see if it is all
zeros. It would be nice if this could use iterate_and_advance() - but
that's currently buried inside lib/iov_iter.c.
Whilst we could provide a generic iteration function that takes a pair
of function pointers instead, it does add around 16% overhead in the
framework, presumably from the combination of function pointers and
various mitigations.
Further, if it is known that just a particular iterator-type is in
play, just that iteration function can be used.
(8) Move the check for ->copy_mc to _copy_from_iter() and
copy_page_from_iter_atomic() rather than in memcpy_from_iter_mc()
where it gets repeated for every segment. Instead, we check once and
invoke a side function that can use iterate_bvec() rather than
iterate_and_advance() and supply a different step function.
(9) Move the copy-and-csum code to net/ where it can be in proximity with
the code that uses it. This eliminates the code if CONFIG_NET=n and
allows for the slim possibility of it being inlined.
(10) Fold memcpy_and_csum() in to its two users.
(11) Move csum_and_copy_from_iter_full() out of line and merge in
csum_and_copy_from_iter() since the former is the only caller of the
latter.
(12) Move hash_and_copy_to_iter() to net/ where it can be with its only
caller.
Anyway, the changes in compiled function size either side of patches
(5)+(6) on x86_64 look like:
__copy_from_iter_mc new 0xe8
_copy_from_iter inc 0x360 -> 0x3a7 +0x47
_copy_from_iter_flushcache inc 0x34c -> 0x38e +0x42
_copy_from_iter_nocache inc 0x354 -> 0x378 +0x24
_copy_mc_to_iter inc 0x396 -> 0x3f1 +0x5b
_copy_to_iter inc 0x33b -> 0x385 +0x4a
copy_page_from_iter_atomic.part.0 inc 0x393 -> 0x3e0 +0x4d
copy_page_to_iter_nofault.part.0 inc 0x3de -> 0x3eb +0xd
copyin del 0x30
copyout del 0x2d
copyout_mc del 0x2b
csum_and_copy_from_iter inc 0x3db -> 0x41d +0x42
csum_and_copy_to_iter inc 0x45d -> 0x48d +0x30
iov_iter_zero inc 0x34a -> 0x36a +0x20
memcpy_from_iter.isra.0 del 0x1f
Note that there's a noticeable expansion on some of the main functions
because a number of the helpers get inlined instead of being called.
In terms of benchmarking patch (5)+(6), three runs without them:
iov_kunit_benchmark_ubuf: avg 3955 uS, stddev 169 uS
iov_kunit_benchmark_ubuf: avg 4122 uS, stddev 1292 uS
iov_kunit_benchmark_ubuf: avg 4451 uS, stddev 1362 uS
iov_kunit_benchmark_iovec: avg 6607 uS, stddev 22 uS
iov_kunit_benchmark_iovec: avg 6608 uS, stddev 19 uS
iov_kunit_benchmark_iovec: avg 6609 uS, stddev 24 uS
iov_kunit_benchmark_bvec: avg 3166 uS, stddev 11 uS
iov_kunit_benchmark_bvec: avg 3167 uS, stddev 13 uS
iov_kunit_benchmark_bvec: avg 3170 uS, stddev 16 uS
iov_kunit_benchmark_bvec_split: avg 3394 uS, stddev 12 uS
iov_kunit_benchmark_bvec_split: avg 3394 uS, stddev 20 uS
iov_kunit_benchmark_bvec_split: avg 3395 uS, stddev 19 uS
iov_kunit_benchmark_kvec: avg 2672 uS, stddev 12 uS
iov_kunit_benchmark_kvec: avg 2672 uS, stddev 12 uS
iov_kunit_benchmark_kvec: avg 2672 uS, stddev 9 uS
iov_kunit_benchmark_xarray: avg 3719 uS, stddev 9 uS
iov_kunit_benchmark_xarray: avg 3719 uS, stddev 9 uS
iov_kunit_benchmark_xarray: avg 3721 uS, stddev 24 uS
and three runs with them:
iov_kunit_benchmark_ubuf: avg 4110 uS, stddev 1254 uS
iov_kunit_benchmark_ubuf: avg 4141 uS, stddev 1411 uS
iov_kunit_benchmark_ubuf: avg 4572 uS, stddev 1889 uS
iov_kunit_benchmark_iovec: avg 6582 uS, stddev 27 uS
iov_kunit_benchmark_iovec: avg 6585 uS, stddev 25 uS
iov_kunit_benchmark_iovec: avg 6586 uS, stddev 48 uS
iov_kunit_benchmark_bvec: avg 3175 uS, stddev 13 uS
iov_kunit_benchmark_bvec: avg 3177 uS, stddev 12 uS
iov_kunit_benchmark_bvec: avg 3178 uS, stddev 12 uS
iov_kunit_benchmark_bvec_split: avg 3380 uS, stddev 20 uS
iov_kunit_benchmark_bvec_split: avg 3384 uS, stddev 15 uS
iov_kunit_benchmark_bvec_split: avg 3386 uS, stddev 25 uS
iov_kunit_benchmark_kvec: avg 2671 uS, stddev 11 uS
iov_kunit_benchmark_kvec: avg 2672 uS, stddev 12 uS
iov_kunit_benchmark_kvec: avg 2677 uS, stddev 20 uS
iov_kunit_benchmark_xarray: avg 3599 uS, stddev 20 uS
iov_kunit_benchmark_xarray: avg 3603 uS, stddev 8 uS
iov_kunit_benchmark_xarray: avg 3610 uS, stddev 16 uS
I've pushed the patches here also:
https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=iov-cleanup
David
Changes
=======
ver #7)
- Defer the patch to add a kernel-backed iter-only to my ceph branch.
- Add missing sign-offs and cc's to commit descriptions.
ver #6)
- Rebase on v6.6-rc2 rather than on my iov-kunit branch.
- Add a patch to remove last_offset from iov_iter.
- Add a patch to tag copy_mc_to_user() with __user on x86.
- Document the priv2 arg of iterate_and_advance_kernel().
ver #5)
- Moved kunit test patches out to a separate set.
- Moved "iter->count - progress" into individual iteration subfunctions.
- Fix iterate_iovec() and to update iter->__iovec after subtracting it to
calculate iter->nr_segs.
- Merged the function inlining patch and the move-to-header patch.
- Rearranged the patch order slightly to put the patches to move
networking stuff to net/ last.
- Went back to a simpler patch to special-case ->copy_mc in
_copy_from_iter() and copy_page_from_iter_atomic() before we get to call
iterate_and_advance() so as to reduce the number of checks for this.
ver #4)
- Fix iterate_bvec() and iterate_kvec() to update iter->bvec and
iter->kvec after subtracting it to calculate iter->nr_segs.
- Change iterate_xarray() to use start+progress rather than increasing
start to reduce code size.
- Added patches to move some iteration functions over to net/ as the files
there can #include the iterator framework.
- Added a patch to benchmark the iteration.
- Tried an experimental patch to make copy_from_iter() and similar always
catch MCE.
ver #3)
- Use min_t(size_t,) not min() to avoid a warning on Hexagon.
- Inline all the step functions.
- Added a patch to better handle copy_mc.
ver #2)
- Rebased on top of Willy's changes in linux-next.
- Change the checksum argument to the iteration functions to be a general
void* and use it to pass iter->copy_mc flag to memcpy_from_iter_mc() to
avoid using a function pointer.
- Arrange the end of the iterate_*() functions to look the same to give
the optimiser the best chance.
- Make iterate_and_advance() a wrapper around iterate_and_advance2().
- Adjust iterate_and_advance2() to use if-else-if-else-if-else rather than
switch(), to put ITER_BVEC before KVEC and to mark UBUF and IOVEC as
likely().
- Move "iter->count += progress" into iterate_and_advance2() from the
iterate functions.
- Mark a number of the iterator helpers with __always_inline.
- Fix _copy_from_iter_flushcache() to use memcpy_from_iter_flushcache()
not memcpy_from_iter().
Link: https://lore.kernel.org/r/3710261.1691764329@xxxxxxxxxxxxxxxxxxxxxx/ # v1
Link: https://lore.kernel.org/r/855.1692047347@xxxxxxxxxxxxxxxxxxxxxx/ # v2
Link: https://lore.kernel.org/r/20230816120741.534415-1-dhowells@xxxxxxxxxx/ # v3
Link: https://lore.kernel.org/r/20230913165648.2570623-1-dhowells@xxxxxxxxxx/ # v4
Link: https://lore.kernel.org/r/20230920222231.686275-1-dhowells@xxxxxxxxxx/ # v5
Link: https://lore.kernel.org/r/20230922120227.1173720-1-dhowells@xxxxxxxxxx/ # v6
David Howells (12):
iov_iter: Remove last_offset from iov_iter as it was for ITER_PIPE
iov_iter, x86: Be consistent about the __user tag on copy_mc_to_user()
sound: Fix snd_pcm_readv()/writev() to use iov access functions
infiniband: Use user_backed_iter() to see if iterator is UBUF/IOVEC
iov_iter: Renumber ITER_* constants
iov_iter: Derive user-backedness from the iterator type
iov_iter: Convert iterate*() to inline funcs
iov_iter: Don't deal with iter->copy_mc in memcpy_from_iter_mc()
iov_iter, net: Move csum_and_copy_to/from_iter() to net/
iov_iter, net: Fold in csum_and_memcpy()
iov_iter, net: Merge csum_and_copy_from_iter{,_full}() together
iov_iter, net: Move hash_and_copy_to_iter() to net/
arch/x86/include/asm/uaccess.h | 2 +-
arch/x86/lib/copy_mc.c | 8 +-
drivers/infiniband/hw/hfi1/file_ops.c | 2 +-
drivers/infiniband/hw/qib/qib_file_ops.c | 2 +-
include/linux/iov_iter.h | 274 ++++++++++++++
include/linux/skbuff.h | 3 +
include/linux/uio.h | 34 +-
lib/iov_iter.c | 441 +++++++----------------
net/core/datagram.c | 75 +++-
net/core/skbuff.c | 40 ++
sound/core/pcm_native.c | 4 +-
11 files changed, 544 insertions(+), 341 deletions(-)
create mode 100644 include/linux/iov_iter.h