From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: [PATCH 1/3] pci: VPD access timeout increase Date: Thu, 4 Sep 2008 09:32:35 -0700 Message-ID: <20080904093235.30ade46b@extreme> References: <20080827204626.4b65862f@extreme> <20080828111323.GI7908@solarflare.com> <20080903155713.7fab2e19@extreme> <20080904125219.GJ2772@parisc-linux.org> <20080904141944.GE7908@solarflare.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Matthew Wilcox , Jesse Barnes , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-pci@vger.kernel.org To: Ben Hutchings Return-path: Received: from mail.vyatta.com ([216.93.170.194]:58271 "EHLO mail.vyatta.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751404AbYIDQci (ORCPT ); Thu, 4 Sep 2008 12:32:38 -0400 In-Reply-To: <20080904141944.GE7908@solarflare.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, 4 Sep 2008 15:19:46 +0100 Ben Hutchings wrote: > Matthew Wilcox wrote: > > On Wed, Sep 03, 2008 at 03:57:13PM -0700, Stephen Hemminger wrote: > > > Accessing the VPD area can take a long time. There are comments in the > > > SysKonnect vendor driver that it can take up to 25ms. The existing vpd > > > access code fails consistently on my hardware. It's bad but not that bad more details are: MIN MAX ------------------------------------------------------------------- write 1.8 ms 3.6 ms internal write cyles 0.7 ms 7.0 ms ------------------------------------------------------------------- over all program time 2.5 ms 10.6 ms read 1.3 ms 2.6 ms ------------------------------------------------------------------- over all 3.8 ms 13.2 ms Usable VPD is limited to 2K so worst case read is 27 seconds. Note: there doesn't appear to be an standard for VPD size register in PCI spec, but there is a device specific register. > > Wow, that's slow. If you were to try to read all 32k, it'd take more > > than three minutes! (I presume it doesn't actually have as much as 32k). > > > > > Change the access routines to: > > > * use a mutex rather than spinning with IRQ's disabled and lock held > > > * have a longer timeout > > > * call schedule while spinning to provide some responsivness > > > > I agree with your approach, but have one minor comment: > > > > > - spin_lock_irq(&vpd->lock); > > > + mutex_lock(&vpd->lock); > > > > This should be: > > > > + if (mutex_lock_interruptible(&vpd->lock)) > > + return -EINTR; > [...] > > This is fine for the sysfs case, but not if this is called during device > probe - we don't want signals to modprobe to break device initialisation, > do we? Why not, it makes sense to allow killing a stuck modprobe.