linux-kernel - Re: [PATCH net-next 2/2] net:add socket option for low latency polling

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Message-ID: <1370966332.3252.38.camel@edumazet-glaptop>
Date:	Tue, 11 Jun 2013 08:58:52 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
Cc:	David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Don Skidmore <donald.c.skidmore@...el.com>,
	e1000-devel@...ts.sourceforge.net,
	Willem de Bruijn <willemb@...gle.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	Andi Kleen <andi@...stfloor.org>, HPA <hpa@...or.com>,
	Eilon Greenstien <eilong@...adcom.com>,
	Or Gerlitz <or.gerlitz@...il.com>,
	Amir Vadai <amirv@...lanox.com>,
	Eliezer Tamir <eliezer@...ir.org.il>
Subject: Re: [PATCH net-next 2/2] net:add socket option for low latency
 polling

On Tue, 2013-06-11 at 18:37 +0300, Eliezer Tamir wrote:
> On 11/06/2013 17:45, Eric Dumazet wrote:
> > On Tue, 2013-06-11 at 17:24 +0300, Eliezer Tamir wrote:
> >> adds a socket option for low latency polling.
> >> This allows overriding the global sysctl value with a per-socket one.
> >>
> >> Signed-off-by: Eliezer Tamir <eliezer.tamir@...ux.intel.com>
> >> ---
> >>
> >>
> >> -static inline cycles_t ll_end_time(void)
> >> +static inline cycles_t ll_end_time(struct sock *sk)
> >>   {
> >> -	return TSC_MHZ * ACCESS_ONCE(sysctl_net_ll_poll) + get_cycles();
> >> +	return TSC_MHZ * ACCESS_ONCE(sk->sk_ll_usec) + get_cycles();
> >>   }
> >
> > Hmm, sk_ll_usec is an unsigned int.
> 
> We changed it to an unsigned long in v7, I guess that was gratuitous.
> Re-reading your comments on v6 2/5 I realize a cast would have sufficed.
> Should I send a patch to revert it to an unsigned int?

One sysctl as unsigned long was not a big deal so I was ok with your
change ;)

unsigned int for sk_ll_usec is enough, but using a 32x32->64bit multiply
is probably safer.




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