From: Eliezer Tamir <eliezer.tamir@linux.intel.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Miller <davem@davemloft.net>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Network Development <netdev@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
David Woodhouse <dwmw2@infradead.org>,
Eliezer Tamir <eliezer@tamir.org.il>
Subject: Re: [PATCH net-next] net: rename low latency sockets functions to busy poll
Date: Mon, 08 Jul 2013 22:46:04 +0300 [thread overview]
Message-ID: <51DB16FC.7060003@linux.intel.com> (raw)
In-Reply-To: <CA+55aFwWAmHhYaPWVm7rsqiD9+RhDPpgVC1yWc0oNmP38bty4Q@mail.gmail.com>
On 08/07/2013 22:37, Linus Torvalds wrote:
> On Mon, Jul 8, 2013 at 10:14 AM, Eliezer Tamir
> <eliezer.tamir@linux.intel.com> wrote:
>>
>> I think there is no way for the compiler to know the value of
>> can_busy_loop at compile time. It depends on the replies we get
>> from polling the sockets. ll_flag was there to make sure the compiler
>> will know when things are defined out.
>
> No, my point was that we want to handle the easily seen register test
> first, and not even have to load current().
>
> The compiler may end up scheduling the code to load current anyway,
> but the way you wrote it it's pretty much guaranteed that it will do
> it.
I see. OK.
> In fact, I'd argue for initializing start_time to zero, and have the
> "have we timed out" logic load it only if necessary, rather than
> initializing it based on whether POLL_BUSY_WAIT was set or not.
> Because one common case - even with POLL_BUSY_WAIT - is that we go
> through the loop exactly once, and the data exists on the very first
> try. And that is in fact the case we want to optimize and not do any
> extra work for at all.
>
> So I would actually argue that the whole timeout code might as well be
> something like
>
> unsigned long start_time = 0;
> ...
> if (want_busy_poll && !need_resched()) {
> unsigned long now = busy_poll_sched_clock();
> if (!start_time) {
> start_time = now + sysctl.busypoll;
> continue;
> }
> if (time_before(start_time, now))
> continue;
> }
>
OK.
Thanks,
Eliezer
next prev parent reply other threads:[~2013-07-08 19:46 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-08 13:20 [PATCH net-next] net: rename low latency sockets functions to busy poll Eliezer Tamir
2013-07-08 16:37 ` Linus Torvalds
2013-07-08 17:14 ` Eliezer Tamir
2013-07-08 19:37 ` Linus Torvalds
2013-07-08 19:46 ` Eliezer Tamir [this message]
2013-07-08 19:59 ` Stephen Hemminger
2013-07-08 20:05 ` Stephen Hemminger
2013-07-08 20:10 ` Linus Torvalds
2013-07-09 2:27 ` David Miller
2013-07-09 22:25 ` Jonathan Corbet
2013-07-09 23:06 ` David Miller
2013-07-10 3:29 ` Eliezer Tamir
2013-07-10 4:41 ` David Miller
2013-07-10 5:21 ` Eliezer Tamir
2013-07-10 6:10 ` Eric Dumazet
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