Messages in this thread | | | From | Tyson Thomas <> | Subject | Re: [BUG REPORT] perf tools: x86_64: weight column displays odd memory latency data | Date | Tue, 7 Jun 2022 20:39:50 +0000 |
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Hi Kan,
Thanks for the reply and sharing your output.
However, I have a couple of questions since the output is not what I have expected and appears odd.
* Are you using the OpenMP version? I ask because I don't observe any openMP symbols in your output * Does your computer have enough ram for cg.D? (Your output does not include the iteration results and the perf file is smaller than expected) I observe a similar issue with cg.C.x (cg.C memory requirements are around 8GB)
Regards, Tyson
From: Liang, Kan <kan.liang@linux.intel.com> Sent: Saturday, 4 June 2022 12:03 AM To: Tyson Thomas <tyson.thomas@sydney.edu.au>; linux-kernel@vger.kernel.org <linux-kernel@vger.kernel.org>; linux-perf-users@vger.kernel.org <linux-perf-users@vger.kernel.org> Subject: Re: [BUG REPORT] perf tools: x86_64: weight column displays odd memory latency data
On 6/1/2022 1:03 AM, Tyson Thomas wrote: > Hi Kan, > > Thanks for the reply. > > The exact command used was: perf mem report > > The columns are in order: Overhead, Samples, Local Weight, Memory Access. > The results I sent before are: Overhead, Local Weight and Memory. > > So, to update the table from before, each tuple has a sample of 1, so it is: > > 0.02%,1 ,62515 ,L1 or L1 hit > 0.02%,1 ,54048 ,L1 or L1 hit > 0.02%,1 ,52206 ,L1 or L1 hit > 0.02%,1 ,49831 ,L1 or L1 hit > 0.02%,1 ,49056 ,Local RAM or RAM hit > 0.01%,1 ,40666 ,LFB or LFB hit > 0.01%,1 ,38080 ,L1 or L1 hit > 0.01%,1 ,36772 ,L1 or L1 hit > > So, the weights are absurdly high here. > > I'll give a reply on perf report -D shortly. > > Regards, > Tyson > > > > From: Liang, Kan <kan.liang@linux.intel.com> > Sent: Wednesday, 25 May 2022 12:58 AM > To: Tyson Thomas <tyson.thomas@sydney.edu.au>; linux-kernel@vger.kernel.org <linux-kernel@vger.kernel.org>; linux-perf-users@vger.kernel.org <linux-perf-users@vger.kernel.org> > Subject: Re: [BUG REPORT] perf tools: x86_64: weight column displays odd memory latency data > > > > On 5/22/2022 6:14 PM, Tyson Thomas wrote: >> Hi Kan, Linux-Perf Team >> >> I have observed some odd behaviour within perf when using perf-mem. Specifically the reported latency under the weight column appears to be unreasonably high. >> >> Here is a given sample from a recent test, I find that some of the latencies are close to an unsigned short and I cannot seem to be understand why that would be outside of it being an issue with the perf events. >> >> This can be replicated using a NAS benchmark, specifically cg.D.
I tried the cg.D benchmark on my machine, but I cannot reproduce the issue. The weight looks reasonable.
$ perf mem record ./bin/cg.D.x
NAS Parallel Benchmarks (NPB3.4-OMP) - CG Benchmark
Size: 1500000 Iterations: 100 Number of available threads: 4
^C[ perf record: Woken up 118 times to write data ] [ perf record: Captured and wrote 30.108 MB perf.data (438307 samples) ]
$ perf mem report --stdio # To display the perf.data header info, please use --header/--header-only options. # # # Total Lost Samples: 0 # # Samples: 209K of event 'cpu/mem-loads,ldlat=30/Pu' # Total weight : 56835744 # Sort order : local_weight,mem,sym,dso,symbol_daddr,dso_daddr,snoop,tlb,locked,blocked,local_ins_lat,p_stage_cyc # # Overhead Samples Local Weight Memory access Symbol Shared Object Data Symbol > # ........ ............ ............ ........................ ................................ .................... ............> # 0.01% 66 53 L1 or L1 hit [.] randlc_ cg.D.x [.] 0x00007f> 0.01% 53 58 L1 or L1 hit [.] randlc_ cg.D.x [.] 0x00007f> 0.01% 59 52 L1 or L1 hit [.] randlc_ cg.D.x [.] 0x00007f> 0.00% 53 53 L1 or L1 hit [.] randlc_ cg.D.x [.] 0x00007f> 0.00% 43 65 L1 or L1 hit [.] randlc_ cg.D.x [.] 0x00007f> 0.00% 50 55 L1 or L1 hit [.] randlc_ cg.D.x [.] 0x00007f> 0.00% 51 50 L1 or L1 hit [.] randlc_ cg.D.x [.] 0x00007f> 0.00% 46 55 L1 or L1 hit [.] randlc_ cg.D.x [.] 0x00007f> 0.00% 49 51 L1 or L1 hit [.] randlc_ cg.D.x [.] 0x00007f> 0.00% 1 2496 LFB or LFB hit [.] sparse_ cg.D.x [.] 0x00007f> 0.00% 48 52 L1 or L1 hit [.] randlc_ cg.D.x [.] 0x00007f> 0.00% 1 2441 Local RAM or RAM hit [.] sparse_ cg.D.x [.] 0x00007f> 0.00% 1 2420 LFB or LFB hit [.] sparse_ cg.D.x [.] 0x00007f> 0.00% 1 2415 LFB or LFB hit [.] sparse_ cg.D.x [.] 0x00007f> 0.00% 1 2403 LFB or LFB hit [.] sparse_ cg.D.x [.] 0x00007f> 0.00% 1 2399 LFB or LFB hit [.] sparse_ cg.D.x [.] 0x00007f> 0.00% 1 2390 LFB or LFB hit [.] sparse_ cg.D.x [.] 0x00007f> 0.00% 1 2385 LFB or LFB hit [.] sparse_ cg.D.x [.] 0x00007f> 0.00% 1 2385 LFB or LFB hit [.] sparse_ cg.D.x [.] 0x00007f> 0.00% 1 2378 LFB or LFB hit [.] sparse_ cg.D.x [.] 0x00007f> 0.00% 1 2358 LFB or LFB hit [.] sparse_ cg.D.x [.] 0x00007f>
Thanks, Kan
>> >> I observe the following results in perf mem report (just getting the top 10 results) >> > > > Could you please show me the exact perf command used? > > With my perf mem report, > The first column is the Overhead. > The second column is the number of samples. > The third column is the weight. > The fourth is the Memory access. > > Seems like the weight is missed? > > Could you please check the perf report -D? > It will dump the weight for each Sample. > Does it look correct? > > Thanks, > Kan > >> 0.02% ,62515 ,L1 or L1 hit >> 0.02% ,54048 ,L1 or L1 hit >> 0.02% ,52206 ,L1 or L1 hit >> 0.02% ,49831 ,L1 or L1 hit >> 0.02% ,49056 ,Local RAM or RAM hit >> 0.01% ,40666 ,LFB or LFB hit >> 0.01% ,38080 ,L1 or L1 hit >> 0.01% ,36772 ,L1 or L1 hit >> 0.01% ,36729 ,LFB or LFB hit >> 0.01% ,27101 ,LFB or LFB hit >> >> Is it possible for someone to shed some light on this or am I misunderstanding how the weight column is used here? >> This appears to have been an issue on 5.4, 5.10 and 5.15. I am looking into seeing if it is still present in 5.17 and 5.18. >> >> I've also tried this on different Intel CPUs such as Intel Xeon 6230, i5-1135G7, Intel Xeon 6330 >> >> Any insight or help would be appreciated, >> Tyson
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