I'll clean this one up a little before merging it as per Ryan's email of a week or two ago. New patch today or tomorrow. Even though this is 1/3 the rest of the series should be fine to merge, right Arnd? cheers On Sat, 2006-04-29 at 02:45 +0200, Arnd Bergmann wrote: > Currently the hvc_rtas driver is painfully slow to use. Our "benchmark" is > ls -R /etc, which spits out about 27866 characters. The theoretical maximum > speed would be about 2.2 seconds, the current code takes ~50 seconds. > > The core of the problem is that sometimes when the tty layer asks us to push > characters the firmware isn't able to handle some or all of them, and so > returns an error. The current code sees this and just returns to the tty code > with the buffer half sent. > > There's the khvcd thread which will eventually wake up and try to push more > characters, that will usually work because the firmware's had time to push > the characters out. But the thread only wakes up every 10 milliseconds, which > isn't fast enough. > > There's already code in the hvc_console driver to make the khvcd thread do > a "quick" loop, where it just calls yield() instead of sleeping. The only code > that triggered that behaviour was recently removed though, which I don't > quite understand. > > Still, if we set HVC_POLL_QUICK whenever the push hvc_push() doesn't push all > characters (ie. RTAS blocks), we can get good performance out of the hvc_rtas > backend. With this patch the "benchmark" takes ~2.8 seconds. > > Cc: Ryan Arnold <[email protected]> > Signed-off-by: Michael Ellerman <[email protected]> > Signed-off-by: Arnd Bergmann <[email protected]> > > --- > > drivers/char/hvc_console.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > Index: linus-2.6/drivers/char/hvc_console.c > =================================================================== > --- linus-2.6.orig/drivers/char/hvc_console.c > +++ linus-2.6/drivers/char/hvc_console.c > @@ -570,7 +570,7 @@ static int hvc_poll(struct hvc_struct *h > hvc_push(hp); > /* Reschedule us if still some write pending */ > if (hp->n_outbuf > 0) > - poll_mask |= HVC_POLL_WRITE; > + poll_mask |= HVC_POLL_WRITE | HVC_POLL_QUICK; > > /* No tty attached, just skip */ > tty = hp->tty; > > -- -- Michael Ellerman IBM OzLabs wwweb: http://michael.ellerman.id.au phone: +61 2 6212 1183 (tie line 70 21183) We do not inherit the earth from our ancestors, we borrow it from our children. - S.M.A.R.T Person
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