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Subject: Re: [PATCH 1/1] ppc/crash: Skip spinlocks during crash
From: Leonardo Bras <leonardo@linux.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>, Christophe Leroy
 <christophe.leroy@c-s.fr>
Date: Mon, 30 Mar 2020 11:12:45 -0300
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Cc: Will Deacon <will@kernel.org>, linuxppc-dev@lists.ozlabs.org,
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Hello Peter,=20

On Mon, 2020-03-30 at 13:02 +0200, Peter Zijlstra wrote:
>  		do {
> > > +			if (unlikely(crash_skip_spinlock))
> > > +				return;
> >=20
> > You are adding a test that reads a global var in the middle of a so hot=
 path
> > ? That must kill performance. Can we do different ?
>=20
> This; adding code to a super hot patch like this for an exceptional case
> like the crash handling seems like a very very bad trade to me.
>=20
> One possible solution is to simply write 0 to the affected spinlocks
> after sending the NMI IPI thing, no?

Yes, I agree.
I suggested this on a comment in v2 of this patch:
http://patchwork.ozlabs.org/patch/1262468/



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