From: Michael Ellerman <mpe@ellerman•id.au>
To: Nicholas Piggin <npiggin@gmail•com>, linuxppc-dev@lists•ozlabs.org
Cc: Nicholas Piggin <npiggin@gmail•com>
Subject: Re: [PATCH v3 2/2] powerpc/64s: Make POWER10 and later use pause_short in cpu_relax loops
Date: Tue, 26 Jul 2022 22:52:19 +1000 [thread overview]
Message-ID: <8735eoavek.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <20220720132132.903462-2-npiggin@gmail.com>
Nicholas Piggin <npiggin@gmail•com> writes:
> We want to move away from using SMT prioroty updates for cpu_relax, and
> use a 'wait' instruction which is similar to x86. As well as being a
> much better fit for what everybody else uses and tests with, priority
> nops are stateful which is nasty (interrupts have to consider they might
> be taken at a different priority), and they're expensive to execute,
> similar to a mtSPR which can effect other threads in the pipe.
>
> Signed-off-by: Nicholas Piggin <npiggin@gmail•com>
> ---
> Unfortunately qemu TCG does not emulate pause_short properly and will
> cause hangs.
That _really_ sucks for testing, being able to use qemu is a huge
benefit. I can boot test multiple kernels per minute using qemu, vs
multiple minutes per kernel using real hardware.
> I have a patch for it but not merged yet. But if we tune
> qspinlock code it would be best to do it with this patch.
What's the urgency on this patch? Can we wait for the qemu change to
land? I guess Qemu 8 is not due until next year? :/
cheers
next prev parent reply other threads:[~2022-07-26 12:53 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-20 13:21 [PATCH v3 1/2] powerpc: add ISA v3.0 / v3.1 wait opcode macro Nicholas Piggin
2022-07-20 13:21 ` [PATCH v3 2/2] powerpc/64s: Make POWER10 and later use pause_short in cpu_relax loops Nicholas Piggin
2022-07-20 21:02 ` Segher Boessenkool
2022-07-26 12:52 ` Michael Ellerman [this message]
2022-07-20 21:07 ` [PATCH v3 1/2] powerpc: add ISA v3.0 / v3.1 wait opcode macro Segher Boessenkool
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