From: Josh Snyder <joshs@netflix.com>
To: Jens Axboe <axboe@kernel.dk>,
Mikulas Patocka <mpatocka@redhat.com>,
Mike Snitzer <snitzer@redhat.com>
Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
Josh Snyder <josh@code406.com>
Subject: [RFC 0/2] Increase accuracy and precision of sampled io_ticks
Date: Mon, 8 Jun 2020 21:07:22 -0700 [thread overview]
Message-ID: <20200609040724.448519-1-joshs@netflix.com> (raw)
Commit 5b18b5a73760 ("block: delete part_round_stats and switch to less
precise counting") introduces a sampling technique for calculating
io_ticks. The sampling algorithm introduces bias in the calculation of
I/O utilization. In my production system, this bias means that a
workload which previously reported 10% I/O utilization now reports 80%.
Patch 1 of this series eliminates the bias.
The sampling technique is also subject to statistical noise. Because it
infers io_ticks based on only 100 samples per second, io_ticks becomes
imprecise, and subject to swings when measuring both random and
deterministic workloads. Patch 2 of this series provides increased
precision by raising the sampling rate.
next reply other threads:[~2020-06-09 4:07 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-09 4:07 Josh Snyder [this message]
2020-06-09 4:07 ` [RFC 1/2] Eliminate over- and under-counting of io_ticks Josh Snyder
2020-06-09 8:08 ` Ming Lei
2020-06-10 1:41 ` Hou Tao
2020-06-10 7:26 ` Josh Snyder
2020-06-09 4:07 ` [RFC 2/2] Track io_ticks at microsecond granularity Josh Snyder
2020-06-09 8:50 ` Ming Lei
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