linux-kernel - Re: [PATCH 2/3] blkio: Add io controller stats like

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Message-ID: <20100402181754.GC3516@redhat.com>
Date:	Fri, 2 Apr 2010 14:17:54 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Divyesh Shah <dpshah@...gle.com>
Cc:	jens.axboe@...cle.com, linux-kernel@...r.kernel.org,
	nauman@...gle.com, ctalbott@...gle.com
Subject: Re: [PATCH 2/3] blkio: Add io controller stats like

On Thu, Apr 01, 2010 at 03:01:24PM -0700, Divyesh Shah wrote:

[..]
> +#define GET_STAT(__VAR, __CONV)						\
> +uint64_t get_##__VAR##_stat(struct blkio_group *blkg, int dummy)	\
> +{									\
> +	uint64_t data = blkg->stats.__VAR;				\
> +	if (__CONV)							\
> +		data = (uint64_t)jiffies_to_msecs(data) * NSEC_PER_MSEC;\
> +	return data;							\
> +}
> +

Hi Divyesh,

I think now you are exporting blkio.time in ns instead of ms? 

- First of all your are breaking ABI.
- Secondly, how does that help. You are capturing all your slice used
  stats in ms. You already lost any ns granularity. What's the point
  in converting these to ns now?
- Does user space software really need that fine grained accounting. If
  this information is used for charging purposes, isn't ms good enough.
 
Thanks
Vivek
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