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

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Date:   Tue, 7 Mar 2023 15:06:10 +0100
From:   Juergen Gross <jgross@...e.com>
To:     David Woodhouse <dwmw2@...radead.org>,
        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 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.


Juergen

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