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>
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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
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