On Thu, Feb 25, 2021 at 09:34:47AM +0100, Christoph Hellwig wrote: > On Thu, Feb 25, 2021 at 08:44:17AM +1100, Dave Chinner wrote: > > > Also, do you have any idea what was Christoph talking about wrt devices > > > with no-op flushes the last time this patch was posted? This change > > > seems straightforward to me (assuming the answers to my two question are > > > 'yes') but I didn't grok what subtlety he was alluding to...? > > > > He was wondering what devices benefited from this. It has no impact > > on highspeed devices that do not require flushes/FUA (e.g. high end > > intel optane SSDs) but those are not the devices this change is > > aimed at. There are no regressions on these high end devices, > > either, so they are largely irrelevant to the patch and what it > > targets... > > I don't think it is that simple. Pretty much every device aimed at > enterprise use does not enable a volatile write cache by default. That > also includes hard drives, arrays and NAND based SSDs. > > Especially for hard drives (or slower arrays) the actual I/O wait might > matter. Sorry, I/O wait might matter for what? I'm really not sure what you're objecting to - you've hand-waved about hardware that doesn't need cache flushes twice now and inferred that they'd be adversely affected by removing cache flushes. That just doesn't make any sense at all, and I have numbers to back it up. You also asked what storage it improved performance on and I told you and then also pointed out all the software layers that it massively helps, too, regardless of the physical storage characteristics. https://lore.kernel.org/linux-xfs/20210203212013.GV4662@xxxxxxxxxxxxxxxxxxx/ I have numbers to back it up. You did not reply to me, so I'm not going to waste time repeating myself here. > What is the argument against making this conditional? There is no argument for making this conditional. You've created an undefined strawman and are demanding that I prove it wrong. If you've got anything concrete, then tell us about it directly and provide numbers. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
