Date: Tue, 4 Jan 2000 23:45:42 +0100 (MET) From: Gerard Roudier <groudier@club-internet.fr> To: Matthew Jacob <mjacob@feral.com> Cc: Adam <bsdx@looksharp.net>, scsi@FreeBSD.ORG Subject: Re: sym troubles Message-ID: <Pine.LNX.3.95.1000104232600.1115A-100000@localhost> In-Reply-To: <Pine.BSF.4.10.10001032109260.3360-100000@beppo.feral.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Mon, 3 Jan 2000, Matthew Jacob wrote: > Not if the xfer size is small enough such that it's held in the drive's > buffer, in which case the bus speed should show up. This may just not happen with some recent devices that are quite aware of modern O/Ses performing proper caching. Throwing away data that have just been read is the right thing to do given common O/Ses caching policy.=20 May-be setting the read retention priority to 0xf in the caching page may ensure such a behaviour. Anyway, I expect smart SCSI devices to throw away just read data from their cache by default. I agree that this worked as you describe with common SCSI-2 devices in the past, but this seem to have changed.=20 If you want to make sure to read from the device cache in your benchmark you may use the LOCK UNLOCK CACHE command with appropriate parameters prior to reading multiple times the corresponding data. G=E9rard. > On Mon, 3 Jan 2000, Adam wrote: >=20 > > Ah. but would this help seeing as how the max speed of a 40x cdrom woul= d > > be 40 * 150kb/sec =3D 6MB/sec? > >=20 > > On Mon, 3 Jan 2000, Matthew Jacob wrote: > >=20 > > > > > >semuta.feral.com > root rdsame /dev/rwd0c 2k 0 1000 > > >Read 2048000 bytes in 0.866316 seconds, 2308.63KB/sec in 2048 byte blo= cks > > >semuta.feral.com > root rdsame /dev/rwd0c 1k 0 10 =20 > > >Read 10240 bytes in 0.6581 seconds, 1519.53KB/sec in 1024 byte blocks > > > > > >... > > > > > >reads from device in blocksize blocks (m or k suffix to indicate KByte= or > > >MByte) starting at seek offset OFFSETBLK repeated NBLKS times. > > > > > > > > >On Mon, 3 Jan 2000, Adam wrote: > > > > > >> (user1)sapphire:/root % ./stuff > > >> Usage: ./stuff device blksize offsetblk nblks > > >> <cluebie> Huh? </cluebie> > > >>=20 > > >> On Mon, 3 Jan 2000, Matthew Jacob wrote: > > >>=20 > > >> > > > >> >Usually drives cache some amount of info- CDs, maybe not. Use the a= ttached > > >> >to find out. > > >> > > > >> > > > >> >> On Mon, 3 Jan 2000, Matthew Jacob wrote: > > >> >/* > > >> > * Copyright (c) 1998, Matthew Jacob > > >>=20 > > > > > > > >=20 >=20 >=20 >=20 > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-scsi" in the body of the message >=20 >=20 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.LNX.3.95.1000104232600.1115A-100000>