Messages in this thread | | | Date | Thu, 30 Mar 2017 11:46:50 +0200 | From | Jesper Dangaard Brouer <> | Subject | Re: in_irq_or_nmi() and RFC patch |
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On Thu, 30 Mar 2017 09:35:02 +0200 Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Mar 30, 2017 at 09:12:23AM +0200, Jesper Dangaard Brouer wrote: > > On Thu, 30 Mar 2017 08:49:58 +0200 > > Peter Zijlstra <peterz@infradead.org> wrote: > > > > > On Wed, Mar 29, 2017 at 09:44:41PM +0200, Jesper Dangaard Brouer wrote: > > > > @@ -2481,7 +2481,11 @@ void free_hot_cold_page(struct page *page, bool cold) > > > > unsigned long pfn = page_to_pfn(page); > > > > int migratetype; > > > > > > > > - if (in_interrupt()) { > > > > + /* > > > > + * Exclude (hard) IRQ and NMI context from using the pcplists. > > > > + * But allow softirq context, via disabling BH. > > > > + */ > > > > + if (in_irq() || irqs_disabled()) { > > > > > > Why do you need irqs_disabled() ? > > > > Because further down I call local_bh_enable(), which calls > > __local_bh_enable_ip() which triggers a warning during early boot on: > > > > WARN_ON_ONCE(in_irq() || irqs_disabled()); > > > > It looks like it is for supporting CONFIG_TRACE_IRQFLAGS. > > Ah, no. Its because when you do things like: > > local_irq_disable(); > local_bh_enable(); > local_irq_enable(); > > you can loose a pending softirq. > > Bugger.. that irqs_disabled() is something we could do without.
Yes, I really don't like adding this irqs_disabled() check here.
> I'm thinking that when tglx finishes his soft irq disable patches for > x86 (same thing ppc also does) we can go revert all these patches. > > Thomas, see: > > https://lkml.kernel.org/r/20170301144845.783f8cad@redhat.com
The summary is Mel and I found a way to optimized the page allocator, by avoiding a local_irq_{save,restore} operation, see commit 374ad05ab64d ("mm, page_alloc: only use per-cpu allocator for irq-safe requests") [1] https://git.kernel.org/davem/net-next/c/374ad05ab64d696
But Tariq discovered that this caused a regression for 100Gbit/s NICs, as the patch excluded softirq from using the per-cpu-page (PCP) lists. As DMA RX page-refill happens in softirq context.
Now we are trying to re-enable allowing softirq to use the PCP. My proposal is: https://lkml.kernel.org/r/20170329214441.08332799@redhat.com The alternative is to revert this optimization.
-- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
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