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[107.191.0.158]) by smtp.gmail.com with ESMTPSA id p84-v6sm908363itc.2.2018.08.02.09.01.24 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 02 Aug 2018 09:01:25 -0700 (PDT) Subject: Re: [PATCH v3] block: make iolatency avg_lat exponentially decay To: Tejun Heo , Dennis Zhou Cc: Josef Bacik , Johannes Weiner , kernel-team@fb.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <20180802061541.49173-1-dennisszhou@gmail.com> <20180802155917.GT1206094@devbig004.ftw2.facebook.com> From: Jens Axboe Message-ID: <2694b782-b28e-3885-660d-a1ee6d00e116@kernel.dk> Date: Thu, 2 Aug 2018 10:01:23 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <20180802155917.GT1206094@devbig004.ftw2.facebook.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/2/18 9:59 AM, Tejun Heo wrote: > Hello, Dennis. > > On Wed, Aug 01, 2018 at 11:15:41PM -0700, Dennis Zhou wrote: >> From: "Dennis Zhou (Facebook)" >> >> Currently, avg_lat is calculated by accumulating the mean of every >> window in a long running cumulative average. As time goes on, the metric >> becomes less and less useful due to the accumulated history. >> >> This patch reuses the same calculation done in load averages to make the >> avg_lat metric more lively. Unlike load averages, the avg only advances >> when a window elapses (due to an io). Idle periods extend the most >> recent window. Bucketing is used to limit the history of avg_lat by >> binding it to the window size. So, the window range for 1/exp (decay >> rate) is [1 min, 2.5 min) when windows elapse immediately. >> >> The current sample window size is exposed in the debug info to enable >> calculation of the window range. >> >> Signed-off-by: Dennis Zhou >> Acked-by: Tejun Heo >> Acked-by: Johannes Weiner >> Acked-by: Josef Bacik > > Heh, sorry about not thinking this up from the beginning but I think > it'd be great to move this to blkcg core so that the stat is always > available regardless of blk-iolatency. It's a really important metric > and can be used for both monitoring and policy implementation. Just make that change a separate patch, since v3 is already applied. -- Jens Axboe