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Re: patch to support output synchronization under -j

From: Tim Murphy
Subject: Re: patch to support output synchronization under -j
Date: Fri, 15 Apr 2011 20:12:13 +0100

I wish I could play with one of those Connection machines and find out
about the bottlenecks at j=0.25*cpus that I can see on some machines



On 15 April 2011 19:32, Howard Chu <address@hidden> wrote:
> Eli Zaretskii wrote:
>>> Date: Fri, 15 Apr 2011 10:37:13 -0400
>>> From: David Boyce<address@hidden>
>>> it's more a question of how many parallel jobs a given make process is
>>> managing since limits on file handles/descriptors are per process.
>> What about people who use "make -j" without limits?
> They're idiots. I've never seen a machine that can handle more than 1.5x
> number of cores without getting bottlenecked by I/O or system scheduler.
> (And I've run this stuff on 1024 node Connection Machines, among other
> things...) Go above a certain threshold and you're only slowing yourself
> down.
>> It's not like having a 256-core machine is a fantasy that will not
>> happen in a few years.  On my day job, we are already using 12 cores
>> and don't consider that "living on the edge".
> We've already seen bug reports from people running on machines with 4096
> cores, trying to run with -j8192 or somesuch. (Default pipe buffer is 4K
> which sets -j4096 as the practical limit without mucking with kernel
> params.)
> --
>  -- Howard Chu
>  CTO, Symas Corp.           http://www.symas.com
>  Director, Highland Sun     http://highlandsun.com/hyc/
>  Chief Architect, OpenLDAP  http://www.openldap.org/project/
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