linux-kernel - Re: [PATCH v6 20/20] irqdomain: Switch to per-domain locking

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Date:   Tue, 07 Mar 2023 14:18:01 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Juergen Gross <jgross@...e.com>,
        Johan Hovold <johan+linaro@...nel.org>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        xen-devel <xen-devel@...ts.xenproject.org>
Cc:     x86@...nel.org, platform-driver-x86@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org, Hsin-Yi Wang <hsinyi@...omium.org>,
        Mark-PK Tsai <mark-pk.tsai@...iatek.com>
Subject: Re: [PATCH v6 20/20] irqdomain: Switch to per-domain locking

On Tue, 2023-03-07 at 15:06 +0100, Juergen Gross wrote:
> On 07.03.23 14:51, David Woodhouse wrote:
> > On Mon, 2023-02-13 at 11:43 +0100, Johan Hovold wrote:
> > > The IRQ domain structures are currently protected by the global
> > > irq_domain_mutex. Switch to using more fine-grained per-domain locking,
> > > which can speed up parallel probing by reducing lock contention.
> > > 
> > > On a recent arm64 laptop, the total time spent waiting for the locks
> > > during boot drops from 160 to 40 ms on average, while the maximum
> > > aggregate wait time drops from 550 to 90 ms over ten runs for example.
> > > 
> > > Note that the domain lock of the root domain (innermost domain) must be
> > > used for hierarchical domains. For non-hierarchical domains (as for root
> > > domains), the new root pointer is set to the domain itself so that
> > > &domain->root->mutex always points to the right lock.
> > > 
> > > Also note that hierarchical domains should be constructed using
> > > irq_domain_create_hierarchy() (or irq_domain_add_hierarchy()) to avoid
> > > having racing allocations access a not fully initialised domain. As a
> > > safeguard, the lockdep assertion in irq_domain_set_mapping() will catch
> > > any offenders that also fail to set the root domain pointer.
> > > 
> > > Tested-by: Hsin-Yi Wang <hsinyi@...omium.org>
> > > Tested-by: Mark-PK Tsai <mark-pk.tsai@...iatek.com>
> > > Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> > 
> > Broke Xen.
> 
> Fixed with commit ad32ab9604f2.

Thanks.

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