linux-kernel - Re: [PATCH v3] block: make iolatency avg

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Date:   Thu, 2 Aug 2018 09:58:32 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Dennis Zhou <dennisszhou@...il.com>, Tejun Heo <tj@...nel.org>,
        Josef Bacik <jbacik@...com>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     kernel-team@...com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] block: make iolatency avg_lat exponentially decay

On 8/2/18 12:15 AM, Dennis Zhou wrote:
> From: "Dennis Zhou (Facebook)" <dennisszhou@...il.com>
> 
> 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.

Applied for 4.19, thanks Dennis.

-- 
Jens Axboe