Skip site navigation (1)Skip section navigation (2)
Date:      Fri, 22 Jun 2018 18:37:50 +0300
From:      Slawa Olhovchenkov <slw@zxy.spb.ru>
To:        Miroslav Lachman <000.fbsd@quip.cz>
Cc:        Warner Losh <imp@bsdimp.com>, FreeBSD-STABLE Mailing List <freebsd-stable@freebsd.org>
Subject:   Re: iostat busy value calculation
Message-ID:  <20180622153750.GA2488@zxy.spb.ru>
In-Reply-To: <55731ed7-c9f5-1e39-9c09-b522e58b97a1@quip.cz>
References:  <98c4156c-d2f0-f0c6-b859-9cea8ec29a42@quip.cz> <CANCZdfqs%2BkJh5MsiGnXUh=9VVNy9qqc3eGCPYftS5gp5nay%2Bxg@mail.gmail.com> <55731ed7-c9f5-1e39-9c09-b522e58b97a1@quip.cz>

next in thread | previous in thread | raw e-mail | index | archive | help
On Wed, Jun 20, 2018 at 07:37:20PM +0200, Miroslav Lachman wrote:

> > %busy comes from the devstat layer. It's defined as the percent of the 
> > time over the polling interval in which at least one transaction was 
> > awaiting completion by the lower layers. It's an imperfect measure of 
> > how busy the drives are (in ye-olden days, before tagged queuing and 
> > NCQ, it was OK because you had THE transaction pending and it was a good 
> > measure of how utilized things were. Now with concurrent I/O in flash 
> > devices, it's only an imperfect approximation).
> 
> Yes, I am aware of this issue. This percentage is just  "is it slightly 
> loaded or heavily loaded" indicator.

for "heavily loaded" use average transaction time and average queue
length



Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20180622153750.GA2488>