Re: [PATCH] perf cs-etm: Remove duplicate and incorrect aux size checks
From: Leo Yan <hidden>
Date: 2021-12-08 13:18:03
Also in:
linux-perf-users, lkml
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
quoted hunk ↗ jump to hunk
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 <redacted> --- 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
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