On Thu, Jun 19 2008, Matthew Wilcox wrote: > Use the noop elevator by default for drives that do not spin > > [Not for applying] > > SSDs do not benefit from the elevator. It just wastes precious CPU cycles. > By selecting the noop elevator by default, we can shave a few microseconds > off each IO. > > I've brazenly stolen sd_vpd_inquiry from mkp's patch here: > > http://marc.info/?l=linux-scsi&m=121264354724277&w=2 > > No need to have two copies of that ... but this will conflict with his code. > > On to the self-criticism: > > I don't intend the final version of this patch to include a printk for > the RPM or even a printk to say we switched IO elevator. I think we're > too verbose in SCSI as it is. > > I think there's an opportunity to improve sd_vpd_inquiry() to remove > some of the duplicate code between sd_set_elevator() and sd_block_limits, > but it's not terribly important. > > The switching of the elevators isn't particularly nice. I assume that > elevator_init("noop") cannot fail, which isn't true. It would be nice > to use the #if 0 block instead, but that causes a null ptr dereference > inside sysfs -- I suspect something isn't set up correctly. I disagree with this approach. For now, lets just add a queue flag that says the device doesn't have a seek penalty and let the io schedulers do what they need to avoid that (it'd be a one-liner change to cfq and as). There's more to io scheduling than just seek reduction, so this is the wrong direction to take imo. -- Jens Axboe -- 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
