From: Matt Redfearn <matt.redfearn@imgtec.com>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Ralf Baechle <ralf@linux-mips.org>, <linux-mips@linux-mips.org>,
Thomas Gleixner <tglx@linutronix.de>,
Paolo Bonzini <pbonzini@redhat.com>,
Chris Metcalf <cmetcalf@mellanox.com>,
Petr Mladek <pmladek@suse.com>,
LKML <linux-kernel@vger.kernel.org>,
James Hogan <james.hogan@imgtec.com>,
Paul Burton <paul.burton@imgtec.com>,
Aaron Tomlin <atomlin@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 1/5] MIPS: Introduce irq_stack
Date: Wed, 7 Dec 2016 09:25:53 +0000 [thread overview]
Message-ID: <09b9fc86-d2ed-6d97-4b46-0d526da68a8c@imgtec.com> (raw)
In-Reply-To: <CAHmME9pFdLALj9sigunS7Uk+NqJi4GcoUGP+Tgpbku0v1ADk=w@mail.gmail.com>
Hi Jason,
On 06/12/16 22:13, Jason A. Donenfeld wrote:
> On Fri, Dec 2, 2016 at 2:39 PM, Matt Redfearn <matt.redfearn@imgtec.com> wrote:
>> +void *irq_stack[NR_CPUS];
> I'm curious why you implemented it this way rather than using
> DEFINE_PER_CPU and the related percpu helper functions.
Because in the IRQ entry point in assembler we have to look up the
address of this CPU's IRQ stack. Doing so with a simple array can be
done with fewer instructions than a per-cpu variable. The kernel stack
pointer for each CPU is held in a similar array.
MIPS does not have a particularly optimized per-cpu implementation with
the per-cpu offset being held somewhere easily accessible, so right now
it has be looked up from the __per_cpu_offset array, and then applied to
the per-cpu pointer. Obviously doing the first lookup is analogous to
what I am doing, and the subsequent application to the per-cpu pointer
would be additional instructions.
Thanks,
Matt
next prev parent reply other threads:[~2016-12-07 9:25 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-02 13:39 [PATCH 0/5] MIPS: Add per-cpu IRQ stack Matt Redfearn
2016-12-02 13:39 ` [PATCH 1/5] MIPS: Introduce irq_stack Matt Redfearn
2016-12-06 22:13 ` Jason A. Donenfeld
2016-12-07 9:25 ` Matt Redfearn [this message]
2016-12-02 13:39 ` [PATCH 2/5] MIPS: Stack unwinding while on IRQ stack Matt Redfearn
2016-12-02 13:39 ` [PATCH 3/5] MIPS: Only change $28 to thread_info if coming from user mode Matt Redfearn
2016-12-05 16:20 ` Maciej W. Rozycki
2016-12-05 16:52 ` Matt Redfearn
2016-12-05 17:22 ` Maciej W. Rozycki
2016-12-05 17:27 ` Paul Burton
2016-12-05 17:41 ` Maciej W. Rozycki
2016-12-02 13:39 ` [PATCH 4/5] MIPS: Switch to the irq_stack in interrupts Matt Redfearn
2016-12-02 13:39 ` [PATCH 5/5] MIPS: Select HAVE_IRQ_EXIT_ON_IRQ_STACK Matt Redfearn
2016-12-06 22:09 ` [PATCH 0/5] MIPS: Add per-cpu IRQ stack Jason A. Donenfeld
2016-12-07 9:30 ` Matt Redfearn
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