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Re: Extreme I/O latency

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: Extreme I/O latency
From: Fredrik Tolf <fredrik@xxxxxxxxxxxxx>
Date: Tue, 2 Oct 2012 16:31:48 +0200 (CEST)
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20121002050806.GO23520@dastard>
References: <alpine.DEB.2.02.1210020338580.3390@xxxxxxxxxxxxxxxxxxx> <20121002022041.GN23520@dastard> <alpine.DEB.2.02.1210020422540.3390@xxxxxxxxxxxxxxxxxxx> <20121002050806.GO23520@dastard>
User-agent: Alpine 2.02 (DEB 1266 2009-07-14)
On Tue, 2 Oct 2012, Dave Chinner wrote:
On Tue, Oct 02, 2012 at 05:25:53AM +0200, Fredrik Tolf wrote:
On Tue, 2 Oct 2012, Dave Chinner wrote:
On Tue, Oct 02, 2012 at 03:53:08AM +0200, Fredrik Tolf wrote:
What is a "simple IO operation"?

Sorry, what I meant by "simple" is mostly on the interface level.
Like, a single syscall (with far less than a page of data in the
case of read or write), or, in this case, reading a single mmap'ed
page.

Which might be "simple" by themselves, but when an application is
doing thousands of such operations a second, the result is far from
simple....

Certainly; though I seem to be bad at communicating it, the point I was trying to make is that it is, from the point of view of userspace, individual calls that take extremely long, rather than total throughput being poor. :)

--

Fredrik Tolf

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