linux-kernel - Re: [PATCH] net: tcp: Fix a PTO timing granularity issue

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Message-ID: <1432738585.4060.392.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 27 May 2015 07:56:25 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ido Yariv <ido@...ery.com>
Cc:	David Laight <David.Laight@...LAB.COM>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	Nandita Dukkipati <nanditad@...gle.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ido Yariv <idox.yariv@...el.com>
Subject: Re: [PATCH] net: tcp: Fix a PTO timing granularity issue

On Wed, 2015-05-27 at 10:40 -0400, Ido Yariv wrote:

> HZ=100 is used on some embedded platforms, so it's still something we
> have to deal with unfortunately..
> 
> Since the '2' here is a lower bound, and msecs_to_jiffies(10) will
> return values greater than 2 for HZ>100 anyway, always ensuring the
> 2 jiffies lower bound shouldn't impact the behavior when HZ=1000.
> 
> However, as far as I can tell, comparing msecs_to_jiffies(10) to 2, or
> comparing the whole timeout to 2 doesn't make much difference, since
> msecs_to_jiffies isn't inlined.
> 
> In other words, keeping the #if shouldn't make much difference in behavior,
> but will save the small comparison.

Yes, I guess David point is to have a macro in include/linux/tcp.h so
that we can have a nice comment, and not having #if ... in a C file.

Maybe other timers in TCP need the same care (I am not asking you to
find them, but having a macro would ease things perhaps)



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