Messages in this thread | | | Date | Fri, 27 Jul 2018 09:06:23 +0200 | From | Jiri Olsa <> | Subject | Re: [PATCH] perf c2c report: Fix crash for empty browser |
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On Thu, Jul 26, 2018 at 11:31:34PM +0000, rodia@autistici.org wrote: > On 2018-07-26 19:30, Arnaldo Carvalho de Melo wrote: > > Em Tue, Jul 24, 2018 at 08:20:08AM +0200, Jiri Olsa escreveu: > > > Do not try to display entry details if there's > > > not any. Currently this ends up in crash: > > > $ perf c2c report > > > perf: Segmentation fault > > > > How to replicate this? > > > > I tried: > > > > $ perf record sleep 1 > > $ perf c2c report > > > > But it didn't segfault > > Similarly I have tried : > $ perf record sleep 1 > $ perf c2c report > Then Press `d` to show the cache-line contents.
yep, sry I forgot to mention you need to press the 'd' to show details
> This replies the segfault on my machine (4.17.8-1). > The patch mentioned above should solve it, even tough I am not sure as I > haven't been able to recompile the kernel.
no need to recompile kernel
> > The segfault by itself seems to be due to the report logic, as it did not > expect to report on an empty browser. > What has stepped me back is that application which I have been testing with > rely on multiple threads instantiated through pthread, which should be > counted in user-level threads right? But they still seem to return an empty > browser.
right, c2c scans read/write accesses and tries to find false sharing cases maybe there was nothing to be found
> When instead c2c is runned system-wide, with an application running on > multiple threads like firefox or julia, cache hits are measured and also > they are traced back in the source code.
I got a cache line (attached) for 'perf bench sched messaging' NOT being traced system wide and just for user (you'll get plenty of detected cachelines in kernel space):
jirka
--- [root@krava perf]# ./perf c2c record --all-user -- ./perf bench sched messaging -l 100000 [root@krava perf]# ./perf c2c report --stdio
================================================= Shared Data Cache Line Table ================================================= # # ----------- Cacheline ---------- Total Tot ----- LLC Load Hitm ----- ---- Store Reference ---- --- Load Dram ---- LLC Total ----- Core Load Hit ----- -- LLC Load Hit -- # Index Address Node PA cnt records Hitm Total Lcl Rmt Total L1Hit L1Miss Lcl Rmt Ld Miss Loads FB L1 L2 Llc Rmt # ..... .................. .... ...... ....... ....... ....... ....... ....... ....... ....... ....... ........ ........ ....... ....... ....... ....... ....... ........ ........ # 0 0x7fff5b729cc0 0 1 44 100.00% 1 1 0 21 21 0 2 0 2 23 0 0 9 11 0
================================================= Shared Cache Line Distribution Pareto ================================================= # # ----- HITM ----- -- Store Refs -- --------- Data address --------- ---------- cycles ---------- Total cpu Shared # Num Rmt Lcl L1 Hit L1 Miss Offset Node PA cnt Pid Code address rmt hitm lcl hitm load records cnt Symbol Object Source:Line Node # ..... ....... ....... ....... ....... .................. .... ...... ....... .................. ........ ........ ........ ....... ........ ............... .................. ..................... .... # ------------------------------------------------------------- 0 0 1 21 0 0x7fff5b729cc0 ------------------------------------------------------------- 0.00% 100.00% 0.00% 0.00% 0x38 0 1 17356 0x7febaf7e1a46 0 142 101 23 4 [.] __libc_read libpthread-2.27.so read.c:28 0 0.00% 0.00% 100.00% 0.00% 0x38 0 1 17356 0x494e4e 0 0 0 21 4 [.] receiver perf sched-messaging.c:129 0
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