[PATCH] Re: linux readahead setting?

[Roger Larsson <roger.larsson@skelleftea.mail.telia.com>]

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On Tuesday 13 November 2001 16:21, Roy Sigurd Karlsbakk wrote:
> Hi
>
> I heard linux does <= 32 page readahead from block devices
> (scsi/ide/que?). Is there a way to double this? I want to read 256kB
> chunks from the SCSI drives, as to get the best speed. These numbers are
> based on some testing and information I've got from Compaq's storage guys.
>
> roy

Note that the interface to /proc/ide/hdX/settings still is buggy...

i.e you should be able to do (in pages):
echo "file_readahead:64" > /proc/ide/hdX/settings
but the result will be a readahead of 128*1024 PAGES... and that
is too much... (even 1024 PAGES is too much)

(after patch, in kB)
echo "file_readahead:256" > /proc/ide/hdX/settings

It is likely that there are more settings in the ide subsystem that is
has this fault... (Andre, I keep repeating myself...)

/RogerL
-- 
Roger Larsson
Skellefteå
Sweden

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*******************************************
Patch prepared by: roger.larsson@norran.net
Name of file: /home/roger/patches/patch-2.4.11-pre2-ide_settings

--- linux/drivers/ide/ide-disk.c.orig	Tue Oct  2 01:05:41 2001
+++ linux/drivers/ide/ide-disk.c	Thu Oct  4 21:15:36 2001
@@ -690,7 +690,7 @@
 	ide_add_setting(drive,	"multcount",		id ? SETTING_RW : SETTING_READ,			HDIO_GET_MULTCOUNT,	HDIO_SET_MULTCOUNT,	TYPE_BYTE,	0,	id ? id->max_multsect : 0,	1,	2,	&drive->mult_count,		set_multcount);
 	ide_add_setting(drive,	"nowerr",		SETTING_RW,					HDIO_GET_NOWERR,	HDIO_SET_NOWERR,	TYPE_BYTE,	0,	1,				1,	1,	&drive->nowerr,			set_nowerr);
 	ide_add_setting(drive,	"breada_readahead",	SETTING_RW,					BLKRAGET,		BLKRASET,		TYPE_INT,	0,	255,				1,	2,	&read_ahead[major],		NULL);
-	ide_add_setting(drive,	"file_readahead",	SETTING_RW,					BLKFRAGET,		BLKFRASET,		TYPE_INTA,	0,	INT_MAX,			1,	1024,	&max_readahead[major][minor],	NULL);
+	ide_add_setting(drive,	"file_readahead",	SETTING_RW,					BLKFRAGET,		BLKFRASET,		TYPE_INTA,	0,	4096,			PAGE_SIZE,	1024,	&max_readahead[major][minor],	NULL);
 	ide_add_setting(drive,	"max_kb_per_request",	SETTING_RW,					BLKSECTGET,		BLKSECTSET,		TYPE_INTA,	1,	255,				1,	2,	&max_sectors[major][minor],	NULL);
 	ide_add_setting(drive,	"lun",			SETTING_RW,					-1,			-1,			TYPE_INT,	0,	7,				1,	1,	&drive->lun,			NULL);
 	ide_add_setting(drive,	"failures",		SETTING_RW,					-1,			-1,			TYPE_INT,	0,	65535,				1,	1,	&drive->failures,		NULL);