I'm sure it was to improve the performance of some SSD we were testing at Spectra.
-- Justin > On Nov 22, 2017, at 9:16 AM, Alan Somers <asom...@freebsd.org> wrote: > > I believe the original motivation was to reduce FLUSH CACHE EXT > activity with some old SSDs that handled that command very slowly. > gibbs might know more. > > On Tue, Nov 21, 2017 at 1:14 PM, Ronald Klop <ronald-li...@klop.ws> wrote: >> Out of curiosity, What is the use case which this improves? Does happen in >> daily usage or mostly in testing? >> >> Regards, >> Ronald. >> >> >> >> On Mon, 20 Nov 2017 23:27:34 +0100, Alan Somers <asom...@freebsd.org> wrote: >> >>> Author: asomers >>> Date: Mon Nov 20 22:27:33 2017 >>> New Revision: 326036 >>> URL: https://svnweb.freebsd.org/changeset/base/326036 >>> >>> Log: >>> da(4): Short-circuit unnecessary BIO_FLUSH commands >>> sys/cam/scsi/scsi_da.c >>> Complete BIO_FLUSH commands immediately if the da(4) device hasn't >>> been written to since the last flush. If we haven't written to the >>> device, there is no reason to send a flush. >>> Submitted by: gibbs >>> Reviewed by: imp >>> MFC after: 3 weeks >>> Sponsored by: Spectra Logic Corp >>> Differential Revision: https://reviews.freebsd.org/D13106 >>> >>> Modified: >>> head/sys/cam/scsi/scsi_da.c >>> >>> Modified: head/sys/cam/scsi/scsi_da.c >>> >>> ============================================================================== >>> --- head/sys/cam/scsi/scsi_da.c Mon Nov 20 22:18:24 2017 (r326035) >>> +++ head/sys/cam/scsi/scsi_da.c Mon Nov 20 22:27:33 2017 (r326036) >>> @@ -3038,6 +3038,18 @@ more: >>> } >>> case BIO_FLUSH: >>> /* >>> + * If we don't support sync cache, or the disk >>> + * isn't dirty, FLUSH is a no-op. Use the >>> + * allocated * CCB for the next bio if one is >>> + * available. >>> + */ >>> + if ((softc->quirks & DA_Q_NO_SYNC_CACHE) != 0 || >>> + (softc->flags & DA_FLAG_DIRTY) == 0) { >>> + biodone(bp); >>> + goto skipstate; >>> + } >>> + >>> + /* >>> * BIO_FLUSH doesn't currently communicate >>> * range data, so we synchronize the cache >>> * over the whole disk. We also force >>> @@ -3052,6 +3064,15 @@ more: >>> /*lb_count*/0, >>> SSD_FULL_SIZE, >>> da_default_timeout*1000); >>> + /* >>> + * Clear the dirty flag before sending the >>> command. >>> + * Either this sync cache will be successful, or >>> it >>> + * will fail after a retry. If it fails, it is >>> + * unlikely to be successful if retried later, so >>> + * we'll save ourselves time by just marking the >>> + * device clean. >>> + */ >>> + softc->flags &= ~DA_FLAG_DIRTY; >>> break; >>> case BIO_ZONE: { >>> int error, queue_ccb; >>> _______________________________________________ >>> svn-src-...@freebsd.org mailing list >>> https://lists.freebsd.org/mailman/listinfo/svn-src-all >>> To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org" > _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
