Mailing-List: contact cygwin-help@sourceware.cygnus.com; run by ezmlm List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner@sources.redhat.com Delivered-To: mailing list cygwin@sources.redhat.com Date: 13 Feb 2001 14:46:12 -0500 Message-ID: <20010213194612.17311.qmail@lizard.curl.com> From: jik-cygwin@curl.com To: dj@delorie.com CC: cygwin@cygwin.com In-reply-to: <200102131935.OAA09136@envy.delorie.com> (message from DJ Delorie on Tue, 13 Feb 2001 14:35:08 -0500) Subject: Re: Optimizing away "ReadFile" calls when Make calls stat() References: <4.3.1.2.20010213134821.019a7130@pop.ma.ultranet.com> <20010213190131.14369.qmail@lizard.curl.com> <200102131935.OAA09136@envy.delorie.com> > Date: Tue, 13 Feb 2001 14:35:08 -0500 > From: DJ Delorie > > I think an easier win would be to cache the bytes read within the > fhandler, not globally, so while each fhandler (i.e. open, stat, > whatnot) would still need to read the file itself, it would never need > to read it more than once. As I've noted separately, reading tens of thousands of files even once incurs a significant performance penalty. The change I've proposed can eliminate reading them at all. > If we still need more performance, perhaps a one-entry cache of the > most recent file accessed (and when) could be added, and ignored if > the data is more than, say, one second old. Even if it were local to > one process, it would hit most of the usual cases (stat a file, alloc > a buffer, then open/read the file). But it does nothing at all for the "usual case" I'm trying to optimize, which is Make stat()ing a file but never reading it. > These should be easier wins (thus, more doable) than a global cache, > which NT should be providing itself as part of the disk cache > subsystem (for local drives, at least). I don't think it's > appropriate for cygwin to go beyond this anyway - too many race > conditions arise. As far as I know, there are no race conditions in the change I suggested. In fact, it *removes* race conditions, since it reduces the number of distinct OS operations that must be performed on a file during stat(). jik -- Want to unsubscribe from this list? Check out: http://cygwin.com/ml/#unsubscribe-simple