From: Ingo Molnar <mingo@kernel.org>
To: Rik van Riel <riel@redhat.com>
Cc: linux-kernel@vger.kernel.org, aquini@redhat.com,
walken@google.com, eric.dumazet@gmail.com, lwoodman@redhat.com,
knoel@redhat.com, chegu_vinod@hp.com,
raghavendra.kt@linux.vnet.ibm.com, mingo@redhat.com
Subject: Re: [PATCH -v4 5/5] x86,smp: limit spinlock delay on virtual machines
Date: Sat, 26 Jan 2013 13:00:43 +0100 [thread overview]
Message-ID: <20130126120043.GB13445@gmail.com> (raw)
In-Reply-To: <20130125141917.6d5960a8@annuminas.surriel.com>
* Rik van Riel <riel@redhat.com> wrote:
> static bool smp_no_nmi_ipi = false;
>
> /*
> + * Modern Intel and AMD CPUs tell the hypervisor when a guest is
> + * spinning excessively on a spinlock. The hypervisor will then
> + * schedule something else, effectively taking care of the backoff
> + * for us. Doing our own backoff on top of the hypervisor's pause
> + * loop exit handling can lead to excessively long delays, and
> + * performance degradations. Limit the spinlock delay in virtual
> + * machines to a smaller value.
> + */
> +#define DELAY_SHIFT 8
> +#define DELAY_FIXED_1 (1<<DELAY_SHIFT)
> +#define MIN_SPINLOCK_DELAY (1 * DELAY_FIXED_1)
> +#define MAX_SPINLOCK_DELAY_NATIVE (16000 * DELAY_FIXED_1)
> +#define MAX_SPINLOCK_DELAY_GUEST (16 * DELAY_FIXED_1)
> +static int __read_mostly max_spinlock_delay = MAX_SPINLOCK_DELAY_NATIVE;
> +void __init init_spinlock_delay(void)
> +{
> + if (x86_hyper)
> + max_spinlock_delay = MAX_SPINLOCK_DELAY_GUEST;
I realize that you took existing code and extended it, but that
chunk of code looks pretty disgusting visually now - at minimum
it should be vertically aligned as most other kernel code does.
The comment should also tell that the unit of these values is
'spinlock-op loops' or so.
Thanks,
Ingo
next prev parent reply other threads:[~2013-01-26 12:00 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-25 19:05 [PATCH -v4 0/5] x86,smp: make ticket spinlock proportional backoff w/ auto tuning Rik van Riel
2013-01-25 19:16 ` [PATCH -v4 1/5] x86,smp: move waiting on contended ticket lock out of line Rik van Riel
2013-01-25 19:17 ` [PATCH -v4 2/5] x86,smp: proportional backoff for ticket spinlocks Rik van Riel
2013-01-25 19:17 ` [PATCH -v4 3/5] x86,smp: auto tune spinlock backoff delay factor Rik van Riel
2013-01-26 12:03 ` Ingo Molnar
2013-01-25 19:18 ` [PATCH -v4 4/5] x86,smp: keep spinlock delay values per hashed spinlock address Rik van Riel
2013-01-27 13:04 ` Michel Lespinasse
2013-02-06 20:10 ` Rik van Riel
2013-02-09 23:50 ` Michel Lespinasse
2013-01-25 19:19 ` [PATCH -v4 5/5] x86,smp: limit spinlock delay on virtual machines Rik van Riel
2013-01-26 12:00 ` Ingo Molnar [this message]
2013-01-26 12:47 ` Borislav Petkov
2013-02-04 13:50 ` Rik van Riel
2013-02-04 14:02 ` Borislav Petkov
2013-02-06 17:05 ` Rik van Riel
2013-01-28 18:18 ` Stefano Stabellini
2013-01-25 19:20 ` [DEBUG PATCH -v4 6/5] x86,smp: add debugging code to track spinlock delay value Rik van Riel
2013-01-26 7:21 ` [PATCH -v4 0/5] x86,smp: make ticket spinlock proportional backoff w/ auto tuning Mike Galbraith
2013-01-26 12:05 ` Ingo Molnar
2013-01-26 13:10 ` Mike Galbraith
2013-01-28 6:49 ` Raghavendra K T
2013-02-03 15:28 ` Chegu Vinod
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