|
xen-devel
[Xen-devel] Re: [PATCH RFC 4/4] xen: implement Xen-specific spinlocks
|
To: |
Johannes Weiner <hannes@xxxxxxxxxxxx> |
|
Subject: |
[Xen-devel] Re: [PATCH RFC 4/4] xen: implement Xen-specific spinlocks |
|
From: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
|
Date: |
Tue, 08 Jul 2008 00:15:21 -0700 |
|
Cc: |
Jens Axboe <axboe@xxxxxxxxx>, Nick Piggin <nickpiggin@xxxxxxxxxxxx>, Xen devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>, Christoph Lameter <clameter@xxxxxxxxxxxxxxxxxxxx>, Petr Tesarik <ptesarik@xxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Thomas Friebel <thomas.friebel@xxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx> |
|
Delivery-date: |
Tue, 08 Jul 2008 00:15:51 -0700 |
|
Envelope-to: |
www-data@xxxxxxxxxxxxxxxxxxx |
|
In-reply-to: |
<87tzf0q3te.fsf@xxxxxxxxxxxx> |
|
List-help: |
<mailto:xen-devel-request@lists.xensource.com?subject=help> |
|
List-id: |
Xen developer discussion <xen-devel.lists.xensource.com> |
|
List-post: |
<mailto:xen-devel@lists.xensource.com> |
|
List-subscribe: |
<http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe> |
|
List-unsubscribe: |
<http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe> |
|
References: |
<20080707190749.299430659@xxxxxxxx> <20080707190838.710151521@xxxxxxxx> <87tzf0q3te.fsf@xxxxxxxxxxxx> |
|
Sender: |
xen-devel-bounces@xxxxxxxxxxxxxxxxxxx |
|
User-agent: |
Thunderbird 2.0.0.14 (X11/20080501) |
Johannes Weiner wrote:
+static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
+static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners);
The plural is a bit misleading, as this is a single pointer per CPU.
Yeah. And it's wrong because it's specifically *not* spinning, but
blocking.
+static noinline void xen_spin_unlock_slow(struct xen_spinlock *xl)
+{
+ int cpu;
+
+ for_each_online_cpu(cpu) {
Would it be feasible to have a bitmap for the spinning CPUs in order to
do a for_each_spinning_cpu() here instead? Or is setting a bit in
spinning_lock() and unsetting it in unspinning_lock() more overhead than
going over all CPUs here?
Not worthwhile, I think. This is a very rare path: it will only happen
if 1) there's lock contention, that 2) wasn't resolved within the
timeout. In practice, this gets called a few thousand times per cpu
over a kernbench, which is nothing.
My very original version of this code kept a bitmask of interested CPUs
within the lock, but there's only space for 24 cpus if we still use a
byte for the lock itself. It all turned out fairly awkward, and this
version is a marked improvement.
J
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel
|
|
|
Home