On Wed, Jun 25 2008, Boaz Harrosh wrote: > Ric Wheeler wrote: > > Jens Axboe wrote: > >> 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. > >> > >> > > Very true - you still will get a significant win by coalescing IO's (say > > for example, to do larger, aligned writes to flash devices). > > > > ric > > > And to not let HUGE writers hug the machine. A scheduler ... Precisely, merging and fairness is a big part of it. Plus, doing this in sd is just a blatant layer violation. -- 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
