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

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Message-ID: <4630B789.3040402@ru.mvista.com>
Date:	Thu, 26 Apr 2007 18:30:33 +0400
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Mike Mattie <codermattie@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org
Subject: Re: htpt366 PCI latency value is really high

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.

   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"...

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

WBR, Sergei
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