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[209.85.221.48]) by smtp.gmail.com with ESMTPSA id e3sm1106456edu.3.2020.02.24.12.55.04 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 Feb 2020 12:55:04 -0800 (PST) Received: by mail-wr1-f48.google.com with SMTP id y17so3263773wrn.6 for ; Mon, 24 Feb 2020 12:55:04 -0800 (PST) X-Received: by 2002:a05:651c:555:: with SMTP id q21mr4381361ljp.241.1582577251146; Mon, 24 Feb 2020 12:47:31 -0800 (PST) MIME-Version: 1.0 References: <20200205123216.GO12867@shao2-debian> <20200205125804.GM14879@hirez.programming.kicks-ass.net> <20200221080325.GA67807@shbuild999.sh.intel.com> <20200221132048.GE652992@krava> <20200223141147.GA53531@shbuild999.sh.intel.com> <20200224003301.GA5061@shbuild999.sh.intel.com> <20200224021915.GC5061@shbuild999.sh.intel.com> In-Reply-To: From: Linus Torvalds Date: Mon, 24 Feb 2020 12:47:14 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [LKP] Re: [perf/x86] 81ec3f3c4c: will-it-scale.per_process_ops -5.5% regression To: Feng Tang , Oleg Nesterov , "Eric W. Biederman" Cc: Jiri Olsa , Peter Zijlstra , kernel test robot , Ingo Molnar , Vince Weaver , Jiri Olsa , Alexander Shishkin , Arnaldo Carvalho de Melo , Arnaldo Carvalho de Melo , "Naveen N. Rao" , Ravi Bangoria , Stephane Eranian , Thomas Gleixner , LKML , lkp@lists.01.org, andi.kleen@intel.com, "Huang, Ying" Content-Type: multipart/mixed; boundary="000000000000e292c5059f587a63" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --000000000000e292c5059f587a63 Content-Type: text/plain; charset="UTF-8" [ Adding a few more people that tend to be involved in signal handling. Just in case - even if they probably don't care ] On Mon, Feb 24, 2020 at 12:09 PM Linus Torvalds wrote: > > TOTALLY UNTESTED patch attached. It may be completely buggy garbage, > but it _looks_ trivial enough. I've tested it, and the profiles on the silly microbenchmark look much nicer. Now it's just the sigpending update shows up, the refcount case clearly still occasionally happens, but it's now in the noise. I made slight changes to the __sigqueue_alloc() case to generate better code: since we now use that atomic_inc_return() anyway, we might as well then use the value that is returned for the RLIMIT_SIGPENDING check too, instead of reading it again. That might avoid another potential cacheline bounce, plus the generated code just looks better. Updated (and now slightly tested!) patch attached. It would be interesting if this is noticeable on your benchmark numbers. I didn't actually _time_ anything, I just looked at profiles. But my setup clearly isn't going to see the horrible contention case anyway, so my timing numbers wouldn't be all that interesting. 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