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