Date: Tue, 27 May 2003 19:59:30 +0400 (MSD) From: Igor Sysoev <is@rambler-co.ru> To: Terry Lambert <tlambert2@mindspring.com> Cc: arch@freebsd.org Subject: Re: sendfile(2) SF_NOPUSH flag proposal Message-ID: <Pine.BSF.4.21.0305271958430.49418-100000@is> In-Reply-To: <3ED3844F.713FB360@mindspring.com>
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On Tue, 27 May 2003, Terry Lambert wrote: > Peter Jeremy wrote: > > On Tue, May 27, 2003 at 11:57:20AM +0400, Igor Sysoev wrote: > > >I thought about it more and I agree with you. TF_NOPUSH should be turned on > > >at the start of a transaction and turned off at the end of a transaction. > > > > > >So I think there should be two flags: > > >SF_NOPUSH - it turns TF_NOPUSH on before the sending. It's cheap: > > >SF_PUSH - it turns TF_NOPUSH off after the sending has been completed. > > > > I agree that the code appears trivial but in order to justify its > > inclusion, you will need to demonstrate that there is some benefit to > > FreeBSD to implement this code. Good justification would be: > > > > 1) The same API is implemented somewhere else (or there is agreement > > between multiple groups to implement it). I don't believe this > > functionality is implemented anywhere else and you've not provided > > any evidence that any other groups are considering such functionality. > > Actually, the functionality can be implemented *without* going > and implementing the API. It should really be contrlled already > by the TCP_NODELAY option *not* having been set by the user, and, > for last-block next-first-block coelescing, by TCP_NOPUSH *having* > been set. It's not an implementing the API. It's an addition to the already existed API - sendfile(2). sendfile(2) already has the flags parameter and this parameter is currently unused and should be zero. I propose two sendfile(2) flags - SF_NOPUSH and SF_PUSH. > > 2) The new feature provides significant performance benefit. In this > > case, I believe the overhead of calling setsockopt(2) is negligible > > so the performance gain would be negligible. > > The overhead of toggling it would be costly. However, I really > don't understand why he isn't just not setting TCP_NODELAY in > the first place, since it's an affirmative option, and then > leaaving the socket alone to act like it's supposed to act. TCP_NODELAY is not set. Igor Sysoev http://sysoev.ru/en/
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