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Message-ID: <46C41C76.1020109@linux.vnet.ibm.com>
Date: Thu, 16 Aug 2007 15:14:22 +0530
From: Balbir Singh <balbir@...ux.vnet.ibm.com>
To: Michael Neuling <mikey@...ling.org>
CC: Paul Mackerras <paulus@...ba.org>, Andrew Morton <akpm@...l.org>,
linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 2/2] [POWERPC] Add scaled time accounting
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@...ling.org>
>
> ---
>
> 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?
> + get_paca()->spurrdelta = get_paca()->purrdelta = 0;
> + account_user_time_scaled(tsk, utimescaled);
> }
>
> static void account_process_time(struct pt_regs *regs)
> @@ -222,6 +249,7 @@ struct cpu_purr_data {
> int initialized; /* thread is running */
> u64 tb; /* last TB value read */
> u64 purr; /* last PURR value read */
> + u64 spurr; /* last SPURR value read */
> };
>
> /*
> Index: linux-2.6-ozlabs/include/asm-powerpc/paca.h
> ===================================================================
> --- linux-2.6-ozlabs.orig/include/asm-powerpc/paca.h
> +++ linux-2.6-ozlabs/include/asm-powerpc/paca.h
> @@ -103,6 +103,9 @@ struct paca_struct {
> u64 user_time; /* accumulated usermode TB ticks */
> u64 system_time; /* accumulated system TB ticks */
> u64 startpurr; /* PURR/TB value snapshot */
> + u64 startspurr; /* SPURR value snapshot */
> + u64 purrdelta; /* FIXME: document */
> + u64 spurrdelta; /* FIXME: document */
> };
>
> extern struct paca_struct paca[];
--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL
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