lkml.org 
[lkml]   [2000]   [Mar]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: new IRQ scalability changes in 2.3.48
On Fri, Mar 03, 2000 at 03:25:23PM +0100, Ingo Molnar wrote:
>
> On Fri, 3 Mar 2000 yodaiken@chelm.cs.nmt.edu wrote:
>
> > On Sun, Feb 27, 2000 at 04:04:13PM +0100, Ingo Molnar wrote:
> > > - per-IRQ-source spinlocks and per-IRQ-controller spinlocks
> > > increasing scalability: now two IRQ handlers on two CPUs
> > > can run do_IRQ in parallel. Note that level-triggered PCI IRQ
> > > handlers never actually take the IRQ-controller spinlock in the
> > > 'IRQ handling fast path'.
> >
> > This change puts spinlock back into the low level irq code -- and I took
> > them out specifically to make RTLinux work and to make Linus happy since
> > he was concerned about minimizing the number of spinlocks. The
> > "optimization" means that you can, in parallel run a tiny section of code
> > that is called infrequently -- [...]
>
> it actually makes a huge difference as the _real_ optimization you missed
> is the lack of cacheline ping-pongs, which pingpong inevitably happens if
> globally shared spinlocks are used.

As in the spin lock in do_IRQ which is still there and now duplicated.
As far as I can see, x86 now does

interrupt:

do_IRQ
spinlock desc->lock
handler->ack
spinlock again

The old code had a spinlock per controller, allowing for
parallel operation. The new code seems to simply duplicate
spin locks.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:56    [from the cache]
©2003-2011 Jasper Spaans