[2175] in linux-scsi channel archive
Re: SG_BIG_BUFF
daemon@ATHENA.MIT.EDU (Kai M{kisara)
Fri Jul 18 03:12:18 1997
Date: Fri, 18 Jul 1997 10:09:53 +0300 (EET DST)
From: Kai M{kisara <makisara@abies.metla.fi>
Reply-To: Kai.Makisara@metla.fi
To: Pete Popov <pete@jones.asd.sel.sony.com>
cc: linux-scsi@vger.rutgers.edu
In-Reply-To: <199707180152.SAA00570@jones.asd.sel.sony.com>
On Thu, 17 Jul 1997, Pete Popov wrote:
>
> Does anyone know if there is any reason why SG_BIG_BUFF is
> limited to 32768 and ST_BUFFER_BLOCKS to 32?
>
I don't want to comment on SG_BIG_BUFF (does not have any effect on tapes
unless you use tapes through generic SCSI) but for ST_BUFFER_BLOCKS being 32
there is a reason: once the buffers are allocated, they are not freed.
This is because there with the current kernel memory allocation method
it may not be possible to reallocate the buffer in future. The value 32
seemed to me like a good compromise between throughput and "wasted"
memory (and still seems so for most cases).
It is completely safe to make ST_BUFFER_BLOCKS as large as the memory
management allows on your hardware (256 for Alphas and 128 for others). If
you want to save memory, you can tune the number of buffers allocated. See
linux/drivers/scsi/README.st for details.
Kai
