linux-kernel - Re: Poor performance on cp on kernel 2.6.27.7-9-xen (openSUSE 11.1)

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Message-ID: <498A430E.1040809@gmail.com>
Date:	Wed, 04 Feb 2009 19:38:22 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Michael Monnerie <michael.monnerie@...it-management.at>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Poor performance on cp on kernel 2.6.27.7-9-xen (openSUSE 11.1)

Michael Monnerie wrote:
> And one last thing:
> rsync -aPv /disk1/bigfile /disk2/xxx
> That copies at max. 50MB/s, because 2 rsync tasks are started each 
> taking 50% of 1 CPU - why doesn't the kernel switch the 2nd task to 
> another CPU? There are 8 cpus in that system - 7 of them idle.

Usually in such cases it's because the tasks are piping data to each 
other in such a way that they can't both run at the same time. In this 
situation there is no point in moving one to another CPU because they're 
not executing concurrently anyway.
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