Date: Thu, 20 Dec 2007 21:40:00 +0100 From: Peter Schuller <peter.schuller@infidyne.com> To: freebsd-fs@freebsd.org, ticso@cicely.de Cc: Ivan Voras <ivoras@freebsd.org> Subject: Re: readv: parallel or sequential? Message-ID: <200712202140.08367.peter.schuller@infidyne.com> In-Reply-To: <20071207174914.GQ10459@cicely12.cicely.de> References: <fjbb3v$n60$1@ger.gmane.org> <fjbk9g$pua$1@ger.gmane.org> <20071207174914.GQ10459@cicely12.cicely.de>
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[-- Attachment #1 --] > Yes, but how can it now that it is on a RAID0 and taking advantage of > multiple spindles instead of making it worse? > The FS has to do sensible things for single spindle as well. > And normaly disks are fastest when reading linear and with disk read > caches this doesn't even have to be interleaved. > I don't see any potential for parallell access within the same file > beside some special constructed cases maybe. I strongly disagree here. I would expect the operating system to not serialize all I/O to the same file descriptor/file, if done in paralell from multiple threads or through AIO. I have at least on use case heavily dependent on this - does this mean FreeBSD would not be usable for this? Not to mention things like databases (e.g. high concurrency I/O in PostgreSQL or whatever). You most definitely want concurrent I/O if supported by the underlying device. Are we saying here that I/O scheduling happens at a just below the file system, rather than at the individual device level? I would have assumed that a particular geom class would just forward (modified) I/O requests to the underlying device, such that when the request reaches a device actually doing I/O to some external entity, it can intelligently schedule in a way that is optimal. Or am I misunderstanding something in this discussion? -- / Peter Schuller PGP userID: 0xE9758B7D or 'Peter Schuller <peter.schuller@infidyne.com>' Key retrieval: Send an E-Mail to getpgpkey@scode.org E-Mail: peter.schuller@infidyne.com Web: http://www.scode.org [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.4 (FreeBSD) iD8DBQBHatMoDNor2+l1i30RAr2LAKCD3H/CKuMJn9ylOddOJNkpdfk2fgCgsVz9 PBPccGBzLdAi7ZeRwaEAjv0= =ZnGO -----END PGP SIGNATURE-----help
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