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 09:28:39 -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 09:25 -0700, Eric Dumazet wrote:

> 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.


Yes, following code is rather crappy :

        if (priv->tx_coal_frames > priv->tx_count_frames) {
                priv->hw->desc->clear_tx_ic(desc);
                priv->xstats.tx_reset_ic_bit++;
                mod_timer(&priv->txtimer,
                          STMMAC_COAL_TIMER(priv->tx_coal_timer));
        } else
                priv->tx_count_frames = 0;

40 ms is already a big timer, and restarting it every time another frame
is queued is a total disaster.



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