Date: Mon, 27 Feb 2006 04:13:19 -0500
From: Shailabh Nagar <nagar@watson.ibm.com>
Subject: Re: [Patch 5/7]  synchronous block I/O delays
In-reply-to: <1141028957.2992.61.camel@laptopd505.fenrus.org>
To: Arjan van de Ven <arjan@infradead.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       lse-tech <lse-tech@lists.sourceforge.net>
Message-id: <4402C2AF.2030008@watson.ibm.com>
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Arjan van de Ven wrote:

>>+static inline void delayacct_blkio(void)
>>+{
>>+	if (unlikely(current->delays && delayacct_on))
>>+		__delayacct_blkio();
>>+}
>>    
>>
>
>why is this unlikely?
>  
>
delayacct_on is expected to be off most of the time, hence the compound is
unlikely too.

>  
>
>>+	u64 blkio_delay;	/* wait for sync block io completion */
>>    
>>
>
>this misses O_SYNC, msync(), and general throttling.
>
Hmm, that it does :-(

>I get the feeling this is being measured at the wrong level
>currently.... since the number of entry points that needs measuring at
>the current level is hardly finite...
>  
>
Will take another look if it can be done elsewhere. Earlier was using 
io_schedule but that isn't
called from everywhere.

--Shailabh
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