Subject: Re: PR/34293 CVS commit: src/sys/dev
To: None <,,>
From: Manuel Bouyer <>
List: netbsd-bugs
Date: 09/06/2006 21:25:01
The following reply was made to PR kern/34293; it has been noted by GNATS.

From: Manuel Bouyer <>
To: Michael van Elst <>
Subject: Re: PR/34293 CVS commit: src/sys/dev
Date: Wed, 6 Sep 2006 23:23:02 +0200

 On Mon, Sep 04, 2006 at 11:23:37PM +0200, Michael van Elst wrote:
 > On Mon, Sep 04, 2006 at 08:55:06PM +0000, Manuel Bouyer wrote:
 > >  > vndstrategy isn't called from interrupt context.
 > >  
 > >  It is, if called from another driver (e.g. Xen block device).
 > I believe that this is not allowed. The strategy routine is
 > part of the top half of the driver, it operates in process
 > context.
 There was a discussion on tech-kern when I introduced the Xen
 backend driver, and the conclusion was that it's valid to call
 a strategy routine from interrupt context, and drivers should deal
 with that.
 > Saying that, I scanned other drivers and found several that may
 > sleep in their strategy() routine. Most promiment scsistrategy()
 > does this (by virtue of calling scsipi_command which waits for
 > a free scsi transfer context in scsipi_get_xs).
 This is a pseudo-strategy, part of the SCSI-specific ioctls implementation.
 It's internal details, it's not exported to other drivers.
 > >  This patch broke vnd for all Xen users, where it worked fine before.
 > I agree. The patch probably leaves a lot space for improvement. But
 > the real bug is calling the strategy() routine from interrupt context.
 You're redefining the strategy() interface here.
 > >  I understand all of this. But 1) the patch is broken (calling tsleep in
 > >  a strategy routine) 2) whenever it's not a problem for other drivers is
 > >  a matter of opinion. If has probably performances inpacts.
 > Calling tsleep() in strategy is allowed.
 Where did you get this ?
 > >  > performances on systems with multiple drives.
 > >  
 > >  No, I meant if all buffers end up in a single device queue.
 > That's what happening without the patch.
 And that's what happens in other driver's queue too.
 Manuel Bouyer <>
      NetBSD: 26 ans d'experience feront toujours la difference