Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Sun, 28 Aug 2016 10:08:45 +0200 | Subject | Re: [PATCH 3/3] scsi/ncr5380: Improve interrupt latency during PIO tranfers |
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Hi Finn,
On Sat, Aug 27, 2016 at 4:30 AM, Finn Thain <fthain@telegraphics.com.au> wrote: > Large PIO transfers are broken up into chunks to try to avoid disabling > local IRQs for long periods. But IRQs are still disabled for too long > and this causes SCC FIFO overruns during serial port transfers. This > patch fixes the problem by halving the PIO chunk size. > > Testing with mac_scsi shows that the extra NCR5380_main() loop iterations > have negligible performance impact on SCSI transfers (about 1% slower). > On a faster system (using the dmx3191d module) transfers showed no > measurable change. > > Signed-off-by: Finn Thain <fthain@telegraphics.com.au> > > --- > drivers/scsi/NCR5380.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > Index: linux/drivers/scsi/NCR5380.c > =================================================================== > --- linux.orig/drivers/scsi/NCR5380.c 2016-08-27 12:29:57.000000000 +1000 > +++ linux/drivers/scsi/NCR5380.c 2016-08-27 12:29:58.000000000 +1000 > @@ -1847,11 +1847,11 @@ static void NCR5380_information_transfer > /* XXX - need to source or sink data here, as appropriate */ > } > } else { > - /* Break up transfer into 3 ms chunks, > - * presuming 6 accesses per handshake. > + /* Transfer a small chunk so that the > + * irq mode lock is not held too long. > */ > transfersize = min((unsigned long)cmd->SCp.this_residual, > - hostdata->accesses_per_ms / 2); > + hostdata->accesses_per_ms >> 2);
I think it's easier to read if you use "/ 4".
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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