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Message-ID: <ZNoeXISDHERwXx5l@chenyu5-mobl2>
Date: Mon, 14 Aug 2023 20:30:20 +0800
From: Chen Yu <yu.c.chen@...el.com>
To: Chris Mason <clm@...a.com>
CC: Peter Zijlstra <peterz@...radead.org>,
David Vernet <void@...ifault.com>,
<linux-kernel@...r.kernel.org>, <kernel-team@...com>,
Ingo Molnar <mingo@...nel.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
<gautham.shenoy@....com>
Subject: Re: schbench v1.0
Hi Chris,
On 2023-04-21 at 14:14:10 -0400, Chris Mason wrote:
> On 4/20/23 11:05 AM, Peter Zijlstra wrote:
> > On Mon, Apr 17, 2023 at 10:10:25AM +0200, Chris Mason wrote:
> >
> >> F128 N10 EEVDF Linus
> >> Wakeup (usec): 99.0th: 755 1,266
> >> Request (usec): 99.0th: 25,632 22,304
> >> RPS (count): 50.0th: 4,280 4,376
> >>
> >> F128 N10 no-locking EEVDF Linus
> >> Wakeup (usec): 99.0th: 823 1,118
> >> Request (usec): 99.0th: 17,184 14,192
> >> RPS (count): 50.0th: 4,440 4,456
> >
> > With the below fixlet (against queue/sched/eevdf) on my measly IVB-EP
> > (2*10*2):
> >
> > ./schbench -F128 -n10 -C
> >
> > Request Latencies percentiles (usec) runtime 30 (s) (153800 total samples)
> > 90.0th: 6376 (35699 samples)
> > * 99.0th: 6440 (9055 samples)
> > 99.9th: 7048 (1345 samples)
> >
> > CFS
> >
> > schbench -m2 -F128 -n10 -r90 OTHER BATCH
> > Wakeup (usec): 99.0th: 6600 6328
> > Request (usec): 99.0th: 35904 14640
> > RPS (count): 50.0th: 5368 6104
> >
>
> Peter and I went back and forth a bit and now schbench git has a few fixes:
>
> - README.md updated
>
> - warmup time defaults to zero (disabling warmup). This was causing the
> stats inconsistency Peter noticed below.
>
> - RPS calculated more often. Every second instead of every reporting
> interval.
>
> - thread count scaled to CPU count when -m is used. The thread count is
> per messenge thread, so when you use -m2 like Peter did in these runs,
> he was ending up with 2xNUM_CPUs workers. That's why his wakeup
> latencies are so high, he had double the work that I did.
>
> I'll experiment with some of the suggestions he made too.
>
Sorry for popping up, while we are doing some eevdf tests and encountered
an issue using the latest schbench, we found this thread. It seems that
there is a minor corner case to be dealt with. Could you help take a look
if the following change make sense?
thanks,
Chenyu
>From e84f7634ab611a560a866c887438a4ebd79935ed Mon Sep 17 00:00:00 2001
From: Chen Yu <yu.c.chen@...el.com>
Date: Mon, 14 Aug 2023 05:00:06 -0700
Subject: [PATCH] schbench: fix per-cpu spin lock
On a system with 1 socket offline, the CPU ids might not
be continuous. The per_cpu_locks is allocated based on the
number of online CPUs but not accessed continuously:
CPU(s): 224
On-line CPU(s) list: 0-55,112-167
Off-line CPU(s) list: 56-111,168-223
The per_cpu_locks is allocated for 112 elements, but be
accessed beyond an index of 112. This could bring unexpected
deadlock during the test.
Fix this by allocating the per_cpu_locks by the number of
possible CPUs, although there could be some waste of space.
Signed-off-by: Chen Yu <yu.c.chen@...el.com>
---
schbench.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/schbench.c b/schbench.c
index 937f1f2..3eaf1a4 100644
--- a/schbench.c
+++ b/schbench.c
@@ -1359,7 +1359,7 @@ int main(int ac, char **av)
matrix_size = sqrt(cache_footprint_kb * 1024 / 3 / sizeof(unsigned long));
- num_cpu_locks = get_nprocs();
+ num_cpu_locks = get_nprocs_conf();
per_cpu_locks = calloc(num_cpu_locks, sizeof(struct per_cpu_lock));
if (!per_cpu_locks) {
perror("unable to allocate memory for per cpu locks\n");
--
2.25.1
> -chris
>
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