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RE: [Xen-devel] [PATCH 3/3] Disable ARB_DIS conditionally

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH 3/3] Disable ARB_DIS conditionally
From: "Wei, Gang" <gang.wei@xxxxxxxxx>
Date: Wed, 3 Sep 2008 23:56:47 +0800
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Thread-topic: [Xen-devel] [PATCH 3/3] Disable ARB_DIS conditionally
Added spinlock just as you suggested. Resend it.


On Wednesday, September 03, 2008 6:40 PM, Keir Fraser wrote:
> On 3/9/08 11:21, "Wei, Gang" <gang.wei@xxxxxxxxx> wrote:
>> CPU0: -------------judge then clear
>> ARB_DIS----------------------------------dec count
>> CPU1: inc count-------------------------------------judge then set ARB_DIS
> Yes, that's a more likely race.
>> Sync via spinlock is good suggest, I need to do some testing to make sure
>> spinlock will not bring larger-than-saved overheads.
> Actually I think it'll be okay. Place the lock next to the c3_cpu_count (so
> they share a cacheline). Something like:
> struct {
>     spinlock_t lock;
>     unsigned int count;
> } c3_cpu_status;
> Then:
>  * Currently: Exclusive access to one cache line + one LOCK prefix
>  * With lock: Exactly the same (since c3_cpu_count no longer needs to be an
> atomic_t, and spin_unlock() is also not a LOCKed instruction).
> But yes, you should test just be to be really sure.
>  -- Keir

Attachment: disable-ARB_DIS-conditionally-0903.patch
Description: disable-ARB_DIS-conditionally-0903.patch

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