linux-kernel - Re: [PATCH 00/10] Stitch LBR call stack

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Message-ID: <20191007182435.GA97660@gmail.com>
Date:   Mon, 7 Oct 2019 20:24:35 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     kan.liang@...ux.intel.com
Cc:     peterz@...radead.org, acme@...nel.org,
        linux-kernel@...r.kernel.org, jolsa@...nel.org,
        namhyung@...nel.org, ak@...ux.intel.com,
        vitaly.slobodskoy@...el.com, pavel.gerasimov@...el.com
Subject: Re: [PATCH 00/10] Stitch LBR call stack


* kan.liang@...ux.intel.com <kan.liang@...ux.intel.com> wrote:

> Performance impact:
> The processing time may increase with the LBR stitching approach
> enabled. The impact depends on the number of samples with stitched LBRs.
> 
> For sqlite's tcltest,
> perf record --call-graph lbr -- make tcltest
> perf report --stitch-lbr
> 
> There are 4.11% samples has stitched LBRs.
> Total number of samples:                        2833728
> The number of samples with stitched LBRs        116478
> 
> The processing time of perf report increases 6.8%
> Without --stitch-lbr:                           55906106 usec
> With --stitch-lbr:                              59728701 usec
> 
> For a simple test case tchain_edit with 43 depth of call stacks.
> perf record --call-graph lbr -- ./tchain_edit
> perf report --stitch-lbr
> 
> There are 99.9% samples has stitched LBRs.
> Total number of samples:                        10915
> The number of samples with stitched LBRs        10905
> 
> The processing time of perf report increases 67.4%
> Without --stitch-lbr:                           11970508 usec
> With --stitch-lbr:                              20036055 usec

That cost seems pretty high, while the feature sounds useful - is there 
any way to speed this up?

Thanks,

	Ingo