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Date:	Wed, 05 Nov 2008 16:10:12 -0700
From:	Andreas Dilger <>
To:	Josef Bacik <>
Subject: Re: [PATCH] imporve jbd2 fsync batching

On Nov 04, 2008  11:10 -0500, Josef Bacik wrote:
> somebody does a sync write or an fsync() traditionally we would sleep for 1
> jiffies, which depending on the value of HZ could be a significant amount of
> time compared to how long it takes to commit a transaction to the underlying
> storage.  With this patch instead of sleeping for a jiffie, we check to see if
> the amount of time this transaction has been running is less than the average
> commit time, and if it is we sleep for the delta using schedule_hrtimeout to
> give us a higher precision sleep time.  This greatly benefits high end storage
> where you could end up sleeping for longer than it takes to commit the
> transaction and therefore sitting idle instead of allowing the transaction to
> be committed by keeping the sleep time to a minimum so you are sure to always
> be doing something.

There was no reply to my previous comments about making the maximum sleep
time be a fixed value (e.g. 15ms) instead of having it arbitrarily based
on the jiffies value, which may change between 1ms and 10ms.

I don't object to this being included in ext4, but I suspect it could do
even better, or at least be more consistent than depending on the HZ value.

Cheers, Andreas
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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