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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 9 May 2023 10:05:01 -0700
Message-ID: <CAHk-=whLZUauRc3skOQGqm3WW4Hr711jHU90dO23ySPFDOFpRA@mail.gmail.com>
Subject: Re: [linus:master] [x86] adfcf4231b: blogbench.read_score -10.9% regression
To:     Feng Tang <feng.tang@intel.com>
Cc:     kernel test robot <yujie.liu@intel.com>,
        Frank Denis <j@pureftpd.org>, oe-lkp@lists.linux.dev,
        lkp@intel.com, linux-kernel@vger.kernel.org, ying.huang@intel.com,
        fengwei.yin@intel.com
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On Tue, May 9, 2023 at 5:30=E2=80=AFAM Feng Tang <feng.tang@intel.com> wrot=
e:
>
> > At a *minimum* that benchmark should have different threads using
> > different read() buffers.
>
> We tried a debug patch which allocates a dedicated buffer for
> each reader thread, run it on the same Cacade Lake platform, and
> the regression is _gone_, after the noise of cache false sharing is
> reduced.

Thanks for verifying.

I was pretty sure that was the issue, but it's always good to
double-check that there wasn't something else going on,

                 Linus