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[209.85.167.51]) by smtp.gmail.com with ESMTPSA id j17sm1165898lfi.43.2018.11.05.09.50.26 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 05 Nov 2018 09:50:26 -0800 (PST) Received: by mail-lf1-f51.google.com with SMTP id v5so1812151lfe.7 for ; Mon, 05 Nov 2018 09:50:26 -0800 (PST) X-Received: by 2002:a19:4948:: with SMTP id l8-v6mr12365873lfj.16.1541440225698; Mon, 05 Nov 2018 09:50:25 -0800 (PST) MIME-Version: 1.0 References: <20181105050813.GP24195@shao2-debian> In-Reply-To: <20181105050813.GP24195@shao2-debian> From: Linus Torvalds Date: Mon, 5 Nov 2018 09:50:09 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [LKP] [mm] 9bc8039e71: will-it-scale.per_thread_ops -64.1% regression To: rong.a.chen@intel.com Cc: yang.shi@linux.alibaba.com, vbabka@suse.cz, kirill.shutemov@linux.intel.com, mhocko@kernel.org, willy@infradead.org, ldufour@linux.vnet.ibm.com, Colin King , Andrew Morton , Linux Kernel Mailing List , lkp@01.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Nov 4, 2018 at 9:08 PM kernel test robot wr= ote: > > FYI, we noticed a -64.1% regression of will-it-scale.per_thread_ops > due to commit 9bc8039e715d ("mm: brk: downgrade mmap_sem to read when > shrinking") Ugh. That looks pretty bad. > in testcase: will-it-scale > on test machine: 8 threads Ivy Bridge with 16G memory > with following parameters: > > nr_task: 100% > mode: thread > test: brk1 > ucode: 0x20 > cpufreq_governor: performance The reason seems to be way more scheduler time due to lots more context switches: > 34925294 =C2=B1 18% +270.3% 1.293e+08 =C2=B1 4% will-it-scale.tim= e.voluntary_context_switches Yang Shi, would you mind taking a look at what's going on? Linus