netdev - Re: Is 3.18 patch "The tcp: TSO packets automatic sizing" will cause to Troughput drop when enable NO_HZ_IDEL or HIGH_RES

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Date:	Wed, 07 May 2014 09:25:39 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	V JobNickname <workofv@...il.com>
Cc:	Neal Cardwell <ncardwell@...gle.com>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: Is 3.18 patch "The tcp: TSO packets automatic sizing" will
 cause to Troughput drop when enable NO_HZ_IDEL or HIGH_RES_TIMERS ?

On Wed, 2014-05-07 at 23:51 +0800, V JobNickname wrote:

> 
> Porting to the v3.15-rc4 from main stream, the performance is well when
>  enabled NO_HZ_IDEL or HIGH_RES_TIMERS.
> 
> I also try the version before commit 740b0f1841f6  tcp: switch rtt
> estimations to usec resolution, i.e
> 363ec392352 net: add skb_mstamp infrastructure,
> also not cause to performance drop. So I think my case is regardless
> to use jiffie or nesc in tcp_update_pacing_rate().
> 
> Then I try more eraly version and found that in 3.14-rc2 thes case was
> hit but solved at 3.14-rc3.
> (I use "git checkout -b 3.14-rc2 v3.14-rc2" and "git checkout -b
> 3.14-rc3 v3.14-rc3"  to get taged version,
> and use "git checkout 3.14-rc2/3.14-rc3 to switch between". Hope my
> usage are correct, since I'm not familer with git.)
> 
> I think some commit between 3.14-rc2 and 3.14-rc3 can help find the
> root cause of my case.
> 
> ps.
> But I don't know how to use git to update from rc2 to rc3 by each
> commit(or maybe binary search commit log), and find that one commit.
> 
> For example, I would like to following logs start from 3.14-rc2 tag in
> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/log/?h=linux-3.14.y&ofs=1650
> 
> Can I,
> 
> git checkout 3.14-rc2 -- switch to 3.14-rc2
> git checout 07b0e5b10258b48e5edfb6c8ac156f05510eb775 (ASoC: da9055:
> Fix device registration of PMIC and CODEC devices)
> will the commit between this commit and 3.14-rc2 also updated?
> if this commit solve my case, I can try some one commit between it and 3.14-rc2.
> such as
> git checkout a49f56eec54d864ba0fda838e4c8bf5c72f3eb08 (microblaze: Fix
> a typo when disabling stack protection)
> should I revert to 3.14-rc2 first, or the git will done it?
> 
> Thanks

I am wondering if you are asking for git bisect maybe ?

https://www.kernel.org/pub/software/scm/git/docs/git-bisect.html

But in this case I am not sure it will help.

An old bug can sit for years, and finally be discovered when some other
change is done.


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