linux-kernel - Re: htpt366 PCI latency value is really high

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Date:	Fri, 27 Apr 2007 23:09:50 -0700
From:	Mike Mattie <codermattie@...il.com>
To:	Sergei Shtylyov <sshtylyov@...mvista.com>
Cc:	lkml <linux-kernel@...r.kernel.org>
Subject: Re: htpt366 PCI latency value is really high

On Thu, 26 Apr 2007 18:30:33 +0400
Sergei Shtylyov <sshtylyov@...mvista.com> wrote:

> Hello.
> 
> Mike Mattie wrote:
> 
> > while hunting down some latency problems I found something quite
> > odd. The latency reported by lspci -v for the HTP203N card is
> > enormous.
> 
> > 00:09.0 RAID bus controller: Triones Technologies, Inc. HPT302/302N
> > (rev 02) Subsystem: Triones Technologies, Inc. Unknown device 0001
> >         Flags: bus master, 66MHz, medium devsel, latency 120, IRQ 17
> >         I/O ports at ec00 [size=8]
> >         I/O ports at e800 [size=4]
> >         I/O ports at e400 [size=8]
> >         I/O ports at e000 [size=4]
> >         I/O ports at dc00 [size=256]
> >         Expansion ROM at dffe0000 [disabled by cmd] [size=128K]
> >         Capabilities: [60] Power Management version 2
> 
> > I am assuming that the "latency" field here is the PCI latency timer
> > which means this card is a bus hog. 
> 
> > From some reading on this issue linux methodically sets a sane
> > value for all the PCI cards it sets up, which looks normal on the
> > rest of the system, which is set to the value: 32
> 
>    Hm, I'm only seeing clamping to the smallest of 64 and
> pcibios_max_latency (255) in arch/i386/pci/i386.c if the latency
> value is too low... Which arch are you using?
> 
> > setting the value 32 with:
> 
> > setpci -v -s "00:09.0" latency_timer=32
> 
> > 00:09.0 RAID bus controller: Triones Technologies, Inc. HPT302/302N
> > (rev 02) Subsystem: Triones Technologies, Inc. Unknown device 0001
> >         Flags: bus master, 66MHz, medium devsel, latency 48, IRQ 17
> >         I/O ports at ec00 [size=8]
> >         I/O ports at e800 [size=4]
> >         I/O ports at e400 [size=8]
> >         I/O ports at e000 [size=4]
> >         I/O ports at dc00 [size=256]
> >         Expansion ROM at dffe0000 [disabled by cmd] [size=128K]
> >         Capabilities: [60] Power Management version 2
> 
> > Results in 48, which is not what I asked, but hopefully this is
> > linux doing the right thing.

output is decimal, input is hex - self-rtfm.
 
>    Not sure -- seems likely that it's the chip's own enforced minimum
> instead...
> 
> > I know this chipset is pretty brain-damaged, but is this
> > high latency value a work-around for broken hardware, or
> 
>    More like it.  Although HighPoint's own drivers force 64.
> 
> > just a oversight ?
> 
>    Not likely since the value is too "special"...

I have ran with a setting of 40 for a couple of days without any trouble.
There are many reasons a card would default to a higher level, but in
the end it is basically tuning the card for a server application.

A warning that some cards default to high PCI latency values; settings that 
can interfere with latency sensitive devices such as sounds cards - this 
could be a help to others.  

00:09.0 RAID bus controller: Triones Technologies, Inc. HPT302/302N
(rev 02) Subsystem: Triones Technologies, Inc. Unknown device 0001
        Flags: bus master, 66MHz, medium devsel, latency 40, IRQ 19
        I/O ports at ec00 [size=8]
        I/O ports at e800 [size=4]
        I/O ports at e400 [size=8]
        I/O ports at e000 [size=4]
        I/O ports at dc00 [size=256]
        Expansion ROM at dffe0000 [disabled by cmd] [size=128K]
        Capabilities: [60] Power Management version 2


> > Cheers,
> > Mike Mattie - codermattie@...il.com
> 
> WBR, Sergei

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