Messages in this thread | | | Date | Fri, 10 Dec 2021 14:55:32 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH] perf cs-etm: Remove dup licate and incorrect aux size checks |
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On December 10, 2021 1:54:36 PM GMT-03:00, Mathieu Poirier <mathieu.poirier@linaro.org> wrote: >On Thu, Dec 09, 2021 at 02:16:43PM +0000, James Clark wrote: >> >> >> On 09/12/2021 13:44, Leo Yan wrote: >> > On Wed, Dec 08, 2021 at 02:08:04PM +0000, James Clark wrote: >> >> On 08/12/2021 13:17, Leo Yan wrote: >> >>> 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? >> >> >> >> Yes that seems to be the case. And the commit message for that addition >> >> states the reasoning: >> >> >> >> perf_counter: Increase mmap limit >> >> >> >> In a default 'perf top' run the tool will create a counter for >> >> each online CPU. With enough CPUs this will eventually exhaust >> >> the default limit. >> >> >> >> So scale it up with the number of online CPUs. >> >> >> >> To me that makes sense. Normally the memory installed also scales with the >> >> number of cores. >> >> >> >> Are you saying that we should look into modifying that scaling factor in >> >> perf_mmap()? Or that we should still add something to userspace for >> >> coresight to limit user supplied buffer sizes? >> > >> > I don't think we should modify the scaling factor in perf_mmap(), the >> > logic is not only used by AUX buffer, it's shared by normal event >> > ring buffer. >> > >> >> I think it makes sense to allow the user to specify any value that will work, >> >> it's up to them. >> > >> > Understand, I verified this patch with below steps: >> > >> > root@debian:~# echo 0 > /proc/sys/kernel/perf_event_paranoid >> > >> > leoy@debian:~$ perf record -e cs_etm// -m 4M,8M -o perf_test.data -- sleep 1 >> > Permission error mapping pages. >> > Consider increasing /proc/sys/kernel/perf_event_mlock_kb, >> > or try again with a smaller value of -m/--mmap_pages. >> > (current value: 1024,2048) >> > >> > leoy@debian:~$ perf record -e cs_etm// -m 4M,4M -o perf_test.data -- sleep 1 >> > Couldn't synthesize bpf events. >> > [ perf record: Woken up 1 times to write data ] >> > [ perf record: Captured and wrote 0.607 MB perf_test.data ] >> > >> > So this patch looks good for me: >> > >> > Reviewed-by: Leo Yan <leo.yan@linaro.org> >> > >> Thanks Leo! > >Arnaldo is not on the recipient list and as such he won't see this patch... >
I saw it now, can I take this as an acked-by: Matthieu too?
- Arnaldo
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