From: Jens Axboe <axboe@kernel.dk>
To: Dave Jiang <dave.jiang@intel.com>
Cc: "fio@vger.kernel.org" <fio@vger.kernel.org>,
"Williams, Dan J" <dan.j.williams@intel.com>
Subject: Re: fio and total latency percentile
Date: Wed, 13 Sep 2017 16:59:03 -0600 [thread overview]
Message-ID: <0c340072-33cc-2171-c149-1ef0b8f94fce@kernel.dk> (raw)
In-Reply-To: <53cbc635-d9a3-6ef3-3634-309db0fe03d5@intel.com>
On 09/07/2017 01:59 PM, Dave Jiang wrote:
> Jens,
> fio can display completion latency percentages via the percentile_list
> parameter. I can get p90 and p99 numbers for clat via
> percentile_list=90:99. Is there a way to get the overall latency for
> percentile? I'm interested in the total latency measurements for p90 and
> p99 while doing some measurements on the persistent memory block driver
> and playing around using DMA engines for transfer.
If I understand correctly, you are using an IO engine that is async, and
you want the latency percentiles to reflect total IO time
(submission+completion), not just completion time?
We can't currently do that, but it'd be trivial to do with an option of
some sort. Currently the percentile enable option is clat_percentile,
and it defaults to on. We could have a lat_percentile option that, if
enabled, would change the reporting to being total IO time. IOW:
clat_percentile=1 Latency percentiles are completion latencies
lat_percentile=1 Latency percentiles are total IO time
and have them be mutually exclusive.
--
Jens Axboe
next prev parent reply other threads:[~2017-09-13 22:59 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-07 19:59 fio and total latency percentile Dave Jiang
2017-09-13 21:10 ` Sitsofe Wheeler
2017-09-13 22:59 ` Jens Axboe [this message]
2017-09-14 4:03 ` Jens Axboe
2017-09-14 4:08 ` Jens Axboe
2017-09-14 16:45 ` Jiang, Dave
2017-09-14 16:46 ` Jens Axboe
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