Date: Thu, 26 Jan 2012 10:43:29 -0800 From: Freddie Cash <fjwcash@gmail.com> To: Artem Belevich <art@freebsd.org> Cc: freebsd-hackers@freebsd.org, =?UTF-8?Q?Edward_Tomasz_Napiera=C5=82a?= <trasz@freebsd.org> Subject: Re: Speeding up the loader(8). Message-ID: <CAOjFWZ7aKLzB5NCqnpXaOuUYJjtHu0isW4YZq2oopjt-t_VqsA@mail.gmail.com> In-Reply-To: <CAFqOu6jRtqNrwJ%2B%2BVDgDtC22CXt-5v8W4h26Y6h43FkWg=nKPw@mail.gmail.com> References: <20120123215503.GA64787@geosci> <CAFqOu6ivT34T_RGHxuWZOTk2mCJ29P6wLY3RHt7=S-wH-Y0eYg@mail.gmail.com> <201201260954.23179.jhb@freebsd.org> <CAFqOu6jRtqNrwJ%2B%2BVDgDtC22CXt-5v8W4h26Y6h43FkWg=nKPw@mail.gmail.com>
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On Thu, Jan 26, 2012 at 10:22 AM, Artem Belevich <art@freebsd.org> wrote: > On Thu, Jan 26, 2012 at 6:54 AM, John Baldwin <jhb@freebsd.org> wrote: >>> > 3. The code in bcache.c doesn't really implement an LRU - it implemen= ts >>> > =C2=A0 'least recently added' algorithm, i.e. a kind of queue. =C2=A0= Not that >>> > =C2=A0 it matters much, since it flushes the elements two seconds aft= er >>> > =C2=A0 caching them anyway. =C2=A0I replaced it with Least Frequently= Used. >>> > =C2=A0 LRU didn't behave well, as it tended to replace metadata with = data >>> > =C2=A0 used only once. >> >> These sound reasonable, though I suspect they are in part due to dealing= with >> floppies where the user can swap out of the disk and we have no way of >> noticing otherwise. =C2=A0However, we could possibly adjust some behavio= r to cache >> the bits if the disk is not a floppy drive. >> >>> 4. it flushes cache on access to a different drive which means that >>> cache does not help on multi-disk ZFS setups. >> >> I believe this is also necessary to deal with floppies and the fact that= you >> don't have a reliable way of knowing if a floppy has changed. > > Are floppies still relevant? > > When I attempted to address your concern about floppies that you > raised when I've sent my patch, I've discovered that there's no floppy > connector on any of the computers/motherboards that I have. > > Few years back I was amused by an Intel motherboard that came with a > floppy disk with RAID drivers on it, but which had no floppy connector > on the motherboard. > > In any case, it's easy enough to enforce old behavior for floppy > drives. I will make required changes but I will not be able to test it > due to lack of floppy drives. USB-based floppy drives are still common. We use them to upgrade firmware, upgrade BIOS, install drivers, etc on our servers ... none of which have floppy headers on the motherboard. But the BIOSes still support floppies, and floppies are still used a lot (unfortunately). Now, whether or not a floppy-based loader would be useful for FreeBSD ... --=20 Freddie Cash fjwcash@gmail.com
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