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Subject: Re: [PATCH 1/2] jbd2: add new tracepoint jbd2_sleep_on_shadow
To:     "Theodore Y. Ts'o" <tytso@mit.edu>
Cc:     linux-ext4@vger.kernel.org
References: <20190902145442.1921-1-xiaoguang.wang@linux.alibaba.com>
 <20190907162145.GC23683@mit.edu>
 <5d96e18f-9610-208f-6db3-6a7b6a112400@linux.alibaba.com>
 <20190911135707.GC2740@mit.edu>
From:   Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Message-ID: <7afa6bc5-71c1-ba8e-5d0b-ea3afc02cd84@linux.alibaba.com>
Date:   Mon, 16 Sep 2019 22:20:54 +0800
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hi,

> On Wed, Sep 11, 2019 at 02:52:51PM +0800, Xiaoguang Wang wrote:
>>> I think maybe it might be better to use units of microseconds and then
>>> change sleep to usleep so the units are clear?  This is a spinlock, so
>>> it should be quick.
>>
>> Sorry, I may not quite understand you, do you mean that milliseconds is not precise, so
>> should use microseconds? For these two patches, they do not use usleep or msleep to do
>> real sleep work, they just record the duration which process takes to wait bh_shadow flag
>> to be cleared or transaction to be unlocked.
> 
> Apologies, I should have been clear enough.  Yes, my concern that
> milliseconds might not be fine-grained enough.  The sample results
> which you showed had values of 2ms, 1ms, and 0ms.  And the single 0ms
> result in particular raised the concern that we should use a
> microseconds instead of milliseconds.
> 
> In fact, instead of "sleep", maybe "latency(us)" or "latency(ms)"
> would be a better label?
OK, I'll update a v2, thanks.

Regards,
Xiaoguang Wang

> 
> Regards,
> 
> 						- Ted
>