Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!edi386!eddjp
From: eddjp@edi386.UUCP ( Dewey Paciaffi )
Newsgroups: comp.benchmarks
Subject: Re: Sparcstation 2 Write I/O
Message-ID: <156@edi386.UUCP>
Date: 18 Feb 91 12:42:25 GMT
References: <152@edi386.UUCP> <1085@rna.UUCP>
Reply-To: eddjp@edi386.UUCP ( Dewey Paciaffi )
Organization: J.M. Huber Corp., Edison,NJ
Lines: 31

In article <1085@rna.UUCP> dan@rna.UUCP (Root Beer) writes:
-In article <152@edi386.UUCP> eddjp@edi386.UUCP ( Dewey Paciaffi ) writes:
->I've found an anomaly I can't explain on my borrowed Sparcstation 2.
->I've been running the Byte Magazine Benchmarks and the file I/O times
->were surprisingly low, around 270 kb / sec. on read and writes.
-
->#include <fcntl.h>
->
->#define BUFFSIZE 1024
-
-	I think your write size is too small. Reads probably benefit greatly
-from the read-ahead of the UNIX buffer cache. But your writes in buffers of
-1024 will not and you'll incur lots of rotational latency (waiting for the
-disk to come around again). Try a buffer of 32768 or more.
-
-					Dan

It was my understanding that the write system call returns as soon as the 
kernel has the data to be written in its buffers. I chose 1024 because
its the size of a file system block and also the size of a buffer cache
block, the buffer cache being made up of a number of these blocks. I
had tried sizes up to 8192 without any observable difference.

I have learned today however that file I/O does not go through the
buffer cache in Sparcs, but rather through the VM system page buffers.
I don't know what effect this has on the way that the write system
call operates.


-- 
Dewey Paciaffi           ...!uunet!edi386!eddjp