Messages in this thread Patch in this message | | | Date | Wed, 8 Dec 2021 21:17:53 +0800 | From | Leo Yan <> | Subject | Re: [PATCH] perf cs-etm: Remove duplicate and incorrect aux size checks |
| |
Hi James,
On Wed, Dec 08, 2021 at 11:54:35AM +0000, James Clark wrote: > There are two checks, one is for size when running without admin, but > this one is covered by the driver and reported on in more detail here > (builtin-record.c): > > pr_err("Permission error mapping pages.\n" > "Consider increasing " > "/proc/sys/kernel/perf_event_mlock_kb,\n" > "or try again with a smaller value of -m/--mmap_pages.\n" > "(current value: %u,%u)\n",
I looked into the kernel code and found:
sysctl_perf_event_mlock = 512 + (PAGE_SIZE / 1024); // 512KB + 1 page
If the system have multiple cores, let's say 8 cores, then kernel even can relax the limitaion with:
user_lock_limit *= num_online_cpus();
So means the memory lock limitation is:
(512KB + 1 page) * 8 = 4MB + 8 pages.
Seems to me, it's much relax than the user space's limitaion 128KB. And let's imagine for Arm server, the permitted buffer size can be a huge value (e.g. for a system with 128 cores).
Could you confirm if this is right?
Thanks, Leo
> This had the effect of artificially limiting the aux buffer size to a > value smaller than what was allowed because perf_event_mlock_kb wasn't > taken into account. > > The second is to check for a power of two, but this is covered here > (evlist.c): > > pr_info("rounding mmap pages size to %s (%lu pages)\n", > buf, pages); > > Signed-off-by: James Clark <james.clark@arm.com> > --- > tools/perf/arch/arm/util/cs-etm.c | 19 ------------------- > 1 file changed, 19 deletions(-) > > diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c > index 293a23bf8be3..8a3d54a86c9c 100644 > --- a/tools/perf/arch/arm/util/cs-etm.c > +++ b/tools/perf/arch/arm/util/cs-etm.c > @@ -407,25 +407,6 @@ static int cs_etm_recording_options(struct auxtrace_record *itr, > > } > > - /* Validate auxtrace_mmap_pages provided by user */ > - if (opts->auxtrace_mmap_pages) { > - unsigned int max_page = (KiB(128) / page_size); > - size_t sz = opts->auxtrace_mmap_pages * (size_t)page_size; > - > - if (!privileged && > - opts->auxtrace_mmap_pages > max_page) { > - opts->auxtrace_mmap_pages = max_page; > - pr_err("auxtrace too big, truncating to %d\n", > - max_page); > - } > - > - if (!is_power_of_2(sz)) { > - pr_err("Invalid mmap size for %s: must be a power of 2\n", > - CORESIGHT_ETM_PMU_NAME); > - return -EINVAL; > - } > - } > - > if (opts->auxtrace_snapshot_mode) > pr_debug2("%s snapshot size: %zu\n", CORESIGHT_ETM_PMU_NAME, > opts->auxtrace_snapshot_size); > -- > 2.28.0 >
| |