Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: Which is simpler? (Was Re: [Suspend2-devel] Re: [ 00/10] [Suspend2] Modules support.) | Date | Mon, 6 Feb 2006 14:45:55 +0100 |
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Hi,
On Monday 06 February 2006 14:04, Jens Axboe wrote: > On Mon, Feb 06 2006, Pavel Machek wrote: > > > > I'll get same bandwidth as you, without need for async I/O. Async I/O > > > > is not really a feature, suspend speed is. (There are existing > > > > interfaces for doing AIO from userspace, anyway, but I'm pretty sure > > > > they will not be needed > > > > > > If you keep writing single pages sync, you sure as hell wont get > > > anywhere near async io in speed... > > > > well, we can perfectly do 128K block... just read 128K into userspace > > buffer, flush it via single write to block device. That should get us > > very close enough to media speed. > > That'll help naturally, 128k sync blocks will be very close to async > performance for most cases. Most cases here being drives with write back > caching enabled, if that is disabled async will still be a big win. > > Is there any reason _not_ to just go with async io? Usually the code is > just as simple (or simpler), since the in-kernel stuff is inherently > async to begin with.
Actually the userland tools we're working on use async I/O. [There's no real need for sync, I think.] Still we write one page at a time, for now, so the I/O performance is not that much better than for the built-in swsusp, but it _is_ better.
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