new kernel = megaraid performance cut in half

new kernel = megaraid performance cut in half

[Matthew Schumacher]

Hello,

I have a dell server that has a perc 3 DCL (megaraid) controller in it 
running redhat 7.2.  I was using the default kernel but I decided to 
upgrade to 2.4.18 to get the new VM code and for some quota fixes. 
Anyway, I compiled the kernel and the machine boots fine but my disk 
speed cut in half.

Is there anything I can do to resolve the speed issue so that I can 
continue using the 2.4.18 kernel?  This box is serving mail so 21MB sec 
on 3x10000rpm scsi3 disks in a raid 5 array is not acceptable.

Thanks for the help,

schu


[root@mail_test linux]# uname -a
Linux mail_test 2.4.18 #1 SMP Mon May 13 18:39:45 AKDT 2002 i686 unknown
[root@mail_test linux]# hdparm -t /dev/sda

/dev/sda:
  Timing buffered disk reads:  64 MB in  3.04 seconds = 21.05 MB/sec


Where on the default redhat kernel I get:

[root@mail_test root]# uname -a
Linux mail_test 2.4.7-10smp #1 SMP Thu Sep 6 17:09:31 EDT 2001 i686 unknown
[root@mail_test root]# hdparm -t /dev/sda

/dev/sda:
  Timing buffered disk reads:  64 MB in  1.71 seconds = 37.43 MB/sec

Re: new kernel = megaraid performance cut in half

[Matthew Schumacher]

Alan,

I am running exactly 1g of ram in the machine.  Is there a way to apply 
those patches manually or should I get the kernel-2.4.18-4.i686.rpm from 
here: http://rhn.redhat.com/errata/RHBA-2002-085.html.

Thanks for the quick response.

schu

Alan Cox wrote:
>>running redhat 7.2.  I was using the default kernel but I decided to 
>>upgrade to 2.4.18 to get the new VM code and for some quota fixes. 
>>Anyway, I compiled the kernel and the machine boots fine but my disk 
>>speed cut in half.
> 
> 
> Do you have large amounts of memory ? The Red Hat kernel includes patches
> that vastly up performance of DMA capable controllers when more than 1Gb
> of RAM is in use.
> 
> Alan

Re: new kernel = megaraid performance cut in half

[Alan Cox]

> running redhat 7.2.  I was using the default kernel but I decided to 
> upgrade to 2.4.18 to get the new VM code and for some quota fixes. 
> Anyway, I compiled the kernel and the machine boots fine but my disk 
> speed cut in half.

Do you have large amounts of memory ? The Red Hat kernel includes patches
that vastly up performance of DMA capable controllers when more than 1Gb
of RAM is in use.

Alan

Re: new kernel = megaraid performance cut in half

[Alan Cox]

> I am running exactly 1g of ram in the machine.  Is there a way to apply 
> those patches manually or should I get the kernel-2.4.18-4.i686.rpm from 
> here: http://rhn.redhat.com/errata/RHBA-2002-085.html.

Your best bet is probably to grab the RH errata kernel. If you get the
source rpm that also includes the patches for some controllers to do
I/O from all of memory.

Hopefully that restores the speed

Re: new kernel = megaraid performance cut in half

[Matthew Schumacher]

Alan,

FYI,

[root@mail_test root]# uname -a
Linux mail_test 2.4.18-4smp #1 SMP Thu May 2 18:32:34 EDT 2002 i686 unknown
[root@mail_test root]# hdparm -t /dev/sda

/dev/sda:
  Timing buffered disk reads:  64 MB in  1.22 seconds = 52.46 MB/sec
[root@mail_test root]# hdparm -t /dev/sda

So the redhat 2.4.18 kernel reads disk almost 2.5 times better on my 
system.... sounds like something that would be handy in a stable kernel 
release.

Thanks for you help,

schu


Alan Cox wrote:
>>I am running exactly 1g of ram in the machine.  Is there a way to apply 
>>those patches manually or should I get the kernel-2.4.18-4.i686.rpm from 
>>here: http://rhn.redhat.com/errata/RHBA-2002-085.html.
> 
> 
> Your best bet is probably to grab the RH errata kernel. If you get the
> source rpm that also includes the patches for some controllers to do
> I/O from all of memory.
> 
> Hopefully that restores the speed

Re: new kernel = megaraid performance cut in half

[Alan Cox]

>   Timing buffered disk reads:  64 MB in  1.22 seconds = 52.46 MB/sec
> [root@mail_test root]# hdparm -t /dev/sda
> 
> So the redhat 2.4.18 kernel reads disk almost 2.5 times better on my 
> system.... sounds like something that would be handy in a stable kernel 
> release.

Agreed, however thats something that really has to be post 2.4.19 so it
gets a lot of testing when merged with the base tree to make sure it has
no dependancies on other changes

Re: new kernel = megaraid performance cut in half

[Mikael Abrahamsson]

On Tue, 14 May 2002, Matthew Schumacher wrote:

> Is there anything I can do to resolve the speed issue so that I can 
> continue using the 2.4.18 kernel?  This box is serving mail so 21MB sec 
> on 3x10000rpm scsi3 disks in a raid 5 array is not acceptable.

I am running 7.3 (upgraded from 7.2) and I feel that the 2.4.18 kernel
with the new VM code is actually inferior to that of 2.4.9-31. I have lots
of memory (1.2 gig) and lots of disk access, and I see more swap and worse
interactive performance on 2.4.18 (redhat supplied kernel) as compared to 
the redhat supplied 2.4.9-31 for 7.2.

-- 
Mikael Abrahamsson    email: swmike@swm.pp.se

Re: new kernel = megaraid performance cut in half

[Matthew Schumacher]

Mikael Abrahamsson wrote:
> On Tue, 14 May 2002, Matthew Schumacher wrote:
> 
> 
>>Is there anything I can do to resolve the speed issue so that I can 
>>continue using the 2.4.18 kernel?  This box is serving mail so 21MB sec 
>>on 3x10000rpm scsi3 disks in a raid 5 array is not acceptable.
> 
> 
> I am running 7.3 (upgraded from 7.2) and I feel that the 2.4.18 kernel
> with the new VM code is actually inferior to that of 2.4.9-31. I have lots
> of memory (1.2 gig) and lots of disk access, and I see more swap and worse
> interactive performance on 2.4.18 (redhat supplied kernel) as compared to 
> the redhat supplied 2.4.9-31 for 7.2.
> 


Hmm, the reason why I upgraded to 2.4.18 in the first place was to fix a 
bunch of problems with quota.  I wonder if 2.4.9-31 will work with the 
quotas correctly, I was on 2.4.7.

schu

Re: new kernel = megaraid performance cut in half

[Alan Cox]

> > I am running 7.3 (upgraded from 7.2) and I feel that the 2.4.18 kernel
> > with the new VM code is actually inferior to that of 2.4.9-31. I have lots
> > of memory (1.2 gig) and lots of disk access, and I see more swap and worse
> > interactive performance on 2.4.18 (redhat supplied kernel) as compared to 
> > the redhat supplied 2.4.9-31 for 7.2.
> 
> Hmm, the reason why I upgraded to 2.4.18 in the first place was to fix a 
> bunch of problems with quota.  I wonder if 2.4.9-31 will work with the 
> quotas correctly, I was on 2.4.7.

Quite a few quota race fixes are after 2.4.9. Its also going to depend
entirely on your workload what works best.

Re: new kernel = megaraid performance cut in half

[Matthew Schumacher]

Alan Cox wrote:
>>>I am running 7.3 (upgraded from 7.2) and I feel that the 2.4.18 kernel
>>>with the new VM code is actually inferior to that of 2.4.9-31. I have lots
>>>of memory (1.2 gig) and lots of disk access, and I see more swap and worse
>>>interactive performance on 2.4.18 (redhat supplied kernel) as compared to 
>>>the redhat supplied 2.4.9-31 for 7.2.
>>
>>Hmm, the reason why I upgraded to 2.4.18 in the first place was to fix a 
>>bunch of problems with quota.  I wonder if 2.4.9-31 will work with the 
>>quotas correctly, I was on 2.4.7.
> 
> 
> Quite a few quota race fixes are after 2.4.9. Its also going to depend
> entirely on your workload what works best.

Hmm, sounds like I am going to go with 2.4.18 on redhat 7.3 then.  I 
really don't want any quota trouble.

schu