linux-kernel - [PATCH v4 0/2] irqchip/gic-v3-its: Balance LPI affinity across CPUs

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Message-Id: <20200515165752.121296-1-maz@kernel.org>
Date:   Fri, 15 May 2020 17:57:50 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     John Garry <john.garry@...wei.com>,
        chenxiang <chenxiang66@...ilicon.com>,
        Zhou Wang <wangzhou1@...ilicon.com>,
        Ming Lei <ming.lei@...hat.com>,
        Jason Cooper <jason@...edaemon.net>,
        Thomas Gleixner <tglx@...utronix.de>, kernel-team@...roid.com
Subject: [PATCH v4 0/2] irqchip/gic-v3-its: Balance LPI affinity across CPUs

When mapping a LPI, the ITS driver picks the first possible
affinity, which is in most cases CPU0, assuming that if
that's not suitable, someone will come and set the affinity
to something more interesting.

It apparently isn't the case, and people complain of poor
performance when many interrupts are glued to the same CPU.
So let's place the interrupts by finding the "least loaded"
CPU (that is, the one that has the fewer LPIs mapped to it).
So called 'managed' interrupts are an interesting case where
the affinity is actually dictated by the kernel itself, and
we should honor this.

* From v3:
  - Always pre-decrement/post-increment affinity to avoid useless
    changes of affinity (John)
  - Don't use the node mask as a superset of the proposed affinity
    as the ACPI tables can't really describe this (John)
  - Rebased on v5.7-rc5

* From v2:
  - Split accounting from CPU selection
  - Track managed and unmanaged interrupts separately

Marc Zyngier (2):
  irqchip/gic-v3-its: Track LPI distribution on a per CPU basis
  irqchip/gic-v3-its: Balance initial LPI affinity across CPUs

 drivers/irqchip/irq-gic-v3-its.c | 170 ++++++++++++++++++++++++++-----
 1 file changed, 143 insertions(+), 27 deletions(-)

-- 
2.26.2