Tony,
On Wed, May 02, 2007 at 12:31:36PM -0500, Tony Ernst wrote:
> This patch fixes the default smpl_entries calculation when using the
> v2.0 perfmon kernel code.
>
> We originally saw this problem when running pfmon on a 16 cpu system.
>
> % /usr/bin/pfmon --system-wide -t 2 --short-smpl-periods=16000000
> number of entries in sampling buffer is zero
> cannot create perfmon context: Invalid argument
> cannot create perfmon context: Invalid argument
> cannot create perfmon context: Invalid argument
> cannot create perfmon context: Invalid argument
> ...
>
> We found that if we limited the number of cpus by adding --cpu-list=0-6,
> it worked. We then discovered that this was related to the locked memory
> ulimit. Setting 'ulimit -l unlimited' allowed it to work on this machine.
>
> Here's the problem. In pfmon_compute_smpl_entries() (pfmon/pfmon_util.c),
> it attemps to dynamically calculate the default number of smpl_entries
> based on the locked memory limit from getrlimit(RLIMIT_MEMLOCK, ...).
> But it appears that this was designed with the newer perfmon kernel code
> in mind, not the v2.0 code (SUSE SLES10) that we are using. In fact, with
> the v2.0 code, locked memory is never used at all, so these calculations
> based on locked memory limit are meaningless. This patch reverts pfmon
I found some references to RLIMIT_MEMLOCK, but I think the current code is
broken
is that it does not seem to update RLIMIT_MEMLOCK.cur when the allocation is
successful. This is gone from v2.4 and also the v2.0 compatbility layer embedded
in it for IA-64.
I am willing to take your pfmon patch but I would also welcome a kernel patch
to correctly manage RLIMIT_MEMLOCK for v2.0.
Thanks for the patch.
> --- pfmon/pfmon/pfmon_util.c 2007-05-01 15:00:56.482141136 -0500
> +++ pfmon/pfmon/pfmon_util.c 2007-05-01 15:04:29.593477171 -0500
> @@ -1170,6 +1170,12 @@
> unsigned long max_entries = 0, orig_smpl_entries = 0;
> size_t pfm_avail, memlock_avail, mem_avail, pgsz;
>
> + if (options.opt_is22 == 0) {
> + if (options.smpl_entries == 0)
> + options.smpl_entries = 2048UL;
> + return 0;
> + }
> +
> pgsz = getpagesize();
> pfm_avail = pfmon_get_perfmon_smpl_mem();
>
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--
-Stephane
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