> -----Original Message----- > From: Andrew Morton [mailto:akpm@xxxxxxxxxxxxxxxxxxxx] > Sent: Tuesday, July 01, 2008 4:23 PM > To: Miller, Mike (OS Dev) > Cc: jens.axboe@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > linux-scsi@xxxxxxxxxxxxxxx > Subject: Re: [PATCH 1/1] cciss: read config to obtain max > outstanding commands per controller > > On Tue, 1 Jul 2008 16:02:47 -0500 > Mike Miller <mike.miller@xxxxxx> wrote: > > > This patch changes the way we determine the maximum number of > > outstanding commands for each controller. Most Smart Array > controllers > > can support up to 1024 commands, the notable exceptions are > the E200 and E200i. > > The next generation of controllers which were just added support a > > mode of operation called Zero Memory Raid (ZMR). In this mode they > > only support 64 outstanding commands. In Full Function Raid > (FFR) mode they support 1024. > > We have been setting the queue depth by arbitrarily assigning some > > value for each controller. We needed a better way to set the queue > > depth to avoid lots of annoying "fifo full" messages. So we > made the > > driver a little smarter. We now read the config table and > subtract 4 > > from the returned value. The -4 is to allow some room for > ioctl calls > > which are not tracked the same way as io commands are tracked. > > What would be the effect of _not_ having this patch upon > users of the new hardware? > > If the answer is "bad" then we should get this change into > 2.6.26 and 2.6.25.x, because people will surely be running > those kernels on the new hardware. Sorry for my late reply, I've been out of the office. Not having this patch would be bad. The performance at a queue depth of 64 is not very good anyway. If we hit the "fifo full" condition we spew annoying messages and spin for a bit and try again. This leads to very poor performance. Thanks, mikem -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
