Date: Mon, 14 May 2001 23:20:56 -0700 From: Alfred Perlstein <bright@wintelcom.net> To: Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp> Cc: jhb@FreeBSD.ORG, current@FreeBSD.ORG Subject: Re: atomic operation of flags (was: RE: select(2) converted to use a condition variable, and optimis) Message-ID: <20010514232056.O2009@fw.wintelcom.net> In-Reply-To: <200105150614.f4F6E0P53295@rina.r.dl.itc.u-tokyo.ac.jp>; from tanimura@r.dl.itc.u-tokyo.ac.jp on Tue, May 15, 2001 at 03:14:00PM %2B0900 References: <200105060731.f467V4g13184@silver.carrots.uucp.r.dl.itc.u-tokyo.ac.jp> <XFMail.010507123722.jhb@FreeBSD.org> <200105150614.f4F6E0P53295@rina.r.dl.itc.u-tokyo.ac.jp>
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* Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp> [010514 23:14] wrote: > On Mon, 07 May 2001 12:37:22 -0700 (PDT), > John Baldwin <jhb@FreeBSD.org> said: > > John> You need the lock when clearing the bit in p_flag. That is why the proc locks > John> are there, so all those proc locks need to stay. When you clear a bit, you are > John> writing all the bits, so you need to ensure that you can atomically > John> read/modify/write all the bits in p_flag, hence the need for the proc lock. > > As we now have a set of atomic operation functions in > machine/atomic.h, why do we not use them to read, modify and write > p_flag atomically? Is that more expensive than protecting by PROC_LOCK > and PROC_UNLOCK? That may be useful as an optimization, however afaik PROC_LOCK covers more than just the flags, if we used atomic ops for the flags and PROC_LOCK for the non-flags stuff it could cause a lot more overhead. -- -Alfred Perlstein - [alfred@freebsd.org] Daemon News Magazine in your snail-mail! http://magazine.daemonnews.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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