Re: [PATCH 2/2] [POWERPC] Add scaled time accounting
From: Michael Neuling
Date: Thu Aug 16 2007 - 19:48:55 EST
In message <46C41C76.1020109@xxxxxxxxxxxxxxxxxx> you wrote:
> Michael Neuling wrote:
> > This adds POWERPC specific hooks for scaled time accounting.
> >
> > POWER6 includes a SPURR register. The SPURR is based off the PURR
> > register but is scaled based on CPU frequency and issue rates. This
> > gives a more accurate account of the instructions used per task. The
> > PURR and timebase will be constant relative to the wall clock,
> > irrespective of the CPU frequency.
> >
> > This implementation reads the SPURR register in account_system_vtime
> > which is only call called on context witch and hard and soft irq entry
> > and exit. The percentage of user and system time is then estimated
> > using the ratio of these accounted by the PURR. If the SPURR is not
> > present, the PURR read.
> >
> > An earlier implementation of this patch read the SPURR whenever the
> > PURR was read, which included the system call entry and exit path.
> > Unfortunately this showed a performance regression on lmbench runs, so
> > was re-implemented.
> >
> > I've included the lmbench results here when run bare metal on POWER6.
> > 1st column is the unpatch results. 2nd column is the results using the
> > below patch and the 3rd is the % diff of these results from the base.
> > 4th and 5th columns are the results and % differnce from the base
> > using the older patch (SPURR read in syscall entry/exit path).
> >
> > Base Scaled-Acct SPURR-in-syscall
> > Result Result % diff Result % diff
> > Simple syscall: 0.3086 0.3086 0.0000 0.3452 11.8600
> > Simple read: 0.4591 0.4671 1.7425 0.5044 9.86713
> > Simple write: 0.4364 0.4366 0.0458 0.4731 8.40971
> > Simple stat: 2.0055 2.0295 1.1967 2.0669 3.06158
> > Simple fstat: 0.5962 0.5876 -1.442 0.6368 6.80979
> > Simple open/close: 3.1283 3.1009 -0.875 3.2088 2.57328
> > Select on 10 fd's: 0.8554 0.8457 -1.133 0.8667 1.32101
> > Select on 100 fd's: 3.5292 3.6329 2.9383 3.6664 3.88756
> > Select on 250 fd's: 7.9097 8.1881 3.5197 8.2242 3.97613
> > Select on 500 fd's: 15.2659 15.836 3.7357 15.873 3.97814
> > Select on 10 tcp fd's: 0.9576 0.9416 -1.670 0.9752 1.83792
> > Select on 100 tcp fd's: 7.248 7.2254 -0.311 7.2685 0.28283
> > Select on 250 tcp fd's: 17.7742 17.707 -0.375 17.749 -0.1406
> > Select on 500 tcp fd's: 35.4258 35.25 -0.496 35.286 -0.3929
> > Signal handler installation: 0.6131 0.6075 -0.913 0.647 5.52927
> > Signal handler overhead: 2.0919 2.1078 0.7600 2.1831 4.35967
> > Protection fault: 0.7345 0.7478 1.8107 0.8031 9.33968
> > Pipe latency: 33.006 16.398 -50.31 33.475 1.42368
> > AF_UNIX sock stream latency: 14.5093 30.910 113.03 30.715 111.692
> > Process fork+exit: 219.8 222.8 1.3648 229.37 4.35623
> > Process fork+execve: 876.14 873.28 -0.32 868.66 -0.8533
> > Process fork+/bin/sh -c: 2830 2876.5 1.6431 2958 4.52296
> > File /var/tmp/XXX write bw: 1193497 1195536 0.1708 118657 -0.5799
> > Pagefaults on /var/tmp/XXX: 3.1272 3.2117 2.7020 3.2521 3.99398
> >
> > Also, kernel compile times show no difference with this patch applied.
> >
> > Signed-off-by: Michael Neuling <mikey@xxxxxxxxxxx>
> >
> > ---
> >
> > arch/powerpc/kernel/asm-offsets.c | 1 +
> > arch/powerpc/kernel/time.c | 32 ++++++++++++++++++++++++++++++--
> > include/asm-powerpc/paca.h | 3 +++
> > 3 files changed, 34 insertions(+), 2 deletions(-)
> >
> > Index: linux-2.6-ozlabs/arch/powerpc/kernel/asm-offsets.c
> > ===================================================================
> > --- linux-2.6-ozlabs.orig/arch/powerpc/kernel/asm-offsets.c
> > +++ linux-2.6-ozlabs/arch/powerpc/kernel/asm-offsets.c
> > @@ -141,6 +141,7 @@ int main(void)
> > DEFINE(PACALPPACAPTR, offsetof(struct paca_struct, lppaca_ptr));
> > DEFINE(PACAHWCPUID, offsetof(struct paca_struct, hw_cpu_id));
> > DEFINE(PACA_STARTPURR, offsetof(struct paca_struct, startpurr));
> > + DEFINE(PACA_STARTSPURR, offsetof(struct paca_struct, startspurr));
> > DEFINE(PACA_USER_TIME, offsetof(struct paca_struct, user_time));
> > DEFINE(PACA_SYSTEM_TIME, offsetof(struct paca_struct, system_time));
> > DEFINE(PACA_SLBSHADOWPTR, offsetof(struct paca_struct, slb_shadow_ptr))
;
> > Index: linux-2.6-ozlabs/arch/powerpc/kernel/time.c
> > ===================================================================
> > --- linux-2.6-ozlabs.orig/arch/powerpc/kernel/time.c
> > +++ linux-2.6-ozlabs/arch/powerpc/kernel/time.c
> > @@ -168,23 +168,44 @@ static u64 read_purr(void)
> > }
> >
> > /*
> > + * Read the SPURR on systems that have it, otherwise the purr
> > + */
> > +static u64 read_spurr(void)
> > +{
> > + if (cpu_has_feature(CPU_FTR_SPURR))
> > + return mfspr(SPRN_SPURR);
> > + return read_purr();
> > +}
> > +
> > +/*
> > * Account time for a transition between system, hard irq
> > * or soft irq state.
> > */
> > void account_system_vtime(struct task_struct *tsk)
> > {
> > - u64 now, delta;
> > + u64 now, nowscaled, delta, deltascaled;
> > unsigned long flags;
> >
> > local_irq_save(flags);
> > now = read_purr();
> > delta = now - get_paca()->startpurr;
> > get_paca()->startpurr = now;
> > + nowscaled = read_spurr();
> > + deltascaled = nowscaled - get_paca()->startspurr;
> > + get_paca()->startspurr = nowscaled;
> > if (!in_interrupt()) {
> > + /* deltascaled includes both user and system time.
> > + * Hence scale it based on the purr ratio to estimate
> > + * the system time */
> > + deltascaled = deltascaled * get_paca()->system_time /
> > + (get_paca()->system_time + get_paca()->user_time);
> > delta += get_paca()->system_time;
> > get_paca()->system_time = 0;
> > }
> > account_system_time(tsk, 0, delta);
> > + get_paca()->purrdelta = delta;
> > + account_system_time_scaled(tsk, deltascaled);
> > + get_paca()->spurrdelta = deltascaled;
> > local_irq_restore(flags);
> > }
> >
> > @@ -196,11 +217,17 @@ void account_system_vtime(struct task_st
> > */
> > void account_process_vtime(struct task_struct *tsk)
> > {
> > - cputime_t utime;
> > + cputime_t utime, utimescaled;
> >
> > utime = get_paca()->user_time;
> > get_paca()->user_time = 0;
> > account_user_time(tsk, utime);
> > +
> > + /* Estimate the scaled utime by scaling the real utime based
> > + * on the last spurr to purr ratio */
> > + utimescaled = utime * get_paca()->spurrdelta / get_paca()->purrdelta;
>
>
> The assumption is account_process_vtime() is always called after
> account_system_vtime(), is my understanding correct?
Yes, we use last spurr/purr ratio grabbed in account_system_vtime to
scale utime appropriately.
Mikey
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