From mboxrd@z Thu Jan  1 00:00:00 1970
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	<0A651ACE-ADD2-4C9F-9491-0802B20923B9@gmail.com>
Date: Thu, 19 Dec 2013 15:16:25 +0100
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From: Gorka Guardiola <paurea@gmail.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
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Subject: Re: [9fans] 9front pegs CPU on VMware
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>
>
> Latency is worse than using mwait because you are sleeping unconditionally.
> Mwait does not prevent you from getting the interrupt to schedule.
>
>
By this I mean that mwait unblocks on interrupt.  You could do something
like
(you do exponential backoff calling sleep or sleep/wakeup in the kernel)
one out of N where N
goes from big to 1 as the count increases:

while(1){
      mwait(&l->mwaitvar);
      test_the_var_and break();
      sleep(0); //one out of N iterations
}

This will make the the process consume a little part of the quantum (until
the next tick)  waiting, and most
of that time the processor is turned off or at least consuming less.

G.

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<div dir=3D"ltr"><div class=3D"gmail_extra"><div class=3D"gmail_quote"><blo=
ckquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #c=
cc solid;padding-left:1ex"><br>
Latency is worse than using mwait because you are sleeping unconditionally.=
<br>
Mwait does not prevent you from getting the interrupt to schedule.<br><br><=
/blockquote><div><br></div><div>By this I mean that mwait unblocks on inter=
rupt. =A0You could do something like</div><div>(you do exponential backoff =
calling sleep or sleep/wakeup in the kernel) one out of N where N</div>
<div>goes from big to 1 as the count increases:</div><div><br></div><div>wh=
ile(1){</div><div>=A0 =A0 =A0 mwait(&amp;l-&gt;mwaitvar);</div><div>=A0 =A0=
 =A0 test_the_var_and break();</div><div>=A0 =A0 =A0 sleep(0); //one out of=
 N iterations</div>
<div>}</div><div><br></div><div>This will make the the process consume a li=
ttle part of the quantum (until the next tick) =A0waiting, and most</div><d=
iv>of that time the processor is turned off or at least consuming less.</di=
v>
<div><br></div><div>G.</div><div><br></div></div>
</div></div>

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