From: Heiko Carstens <heiko.carstens@de.ibm.com>
To: David Hildenbrand <david@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>,
Janosch Frank <frankja@linux.vnet.ibm.com>,
KVM <kvm@vger.kernel.org>, Cornelia Huck <cohuck@redhat.com>,
linux-s390 <linux-s390@vger.kernel.org>
Subject: Re: [PATCH 0/2] KVM: s390: avoid jump tables
Date: Thu, 8 Feb 2018 09:58:19 +0100 [thread overview]
Message-ID: <20180208085819.GC3937@osiris> (raw)
In-Reply-To: <7e9bb181-cec9-0781-03c0-b74d5d087c8a@redhat.com>
On Tue, Feb 06, 2018 at 01:30:28PM +0100, David Hildenbrand wrote:
> On 06.02.2018 12:21, Christian Borntraeger wrote:
> > Some old patches refreshed.
> >
>
> Certainly the right thing to do. Especially also interesting due to
> retpotline (if we get something like that on s390x). If I remember
> correctly, x86 highly benefits by replacing magic function pointer by
> switch statements.
If you look at the generated code for the first patch: gcc now generates
its own jump table which then jumps (indirectly) to a brasl... So it's two
instead of one branch.
I'm not saying that this patch is not good, but there seem be a wrong
assumptions about the benefit here.
next prev parent reply other threads:[~2018-02-08 8:58 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-06 11:21 [PATCH 0/2] KVM: s390: avoid jump tables Christian Borntraeger
2018-02-06 11:21 ` [PATCH 1/2] KVM: s390: use switch vs jump table in priv.c Christian Borntraeger
2018-02-06 12:02 ` Cornelia Huck
2018-02-06 12:32 ` David Hildenbrand
2018-02-08 8:01 ` Heiko Carstens
2018-02-08 9:16 ` Janosch Frank
2018-02-06 11:21 ` [PATCH 2/2] KVM: s390: use switch vs jump table in intercept.c Christian Borntraeger
2018-02-06 12:04 ` Cornelia Huck
2018-02-06 12:05 ` Christian Borntraeger
2018-02-06 12:34 ` David Hildenbrand
2018-02-06 12:47 ` [PATCH v2 " Christian Borntraeger
2018-02-06 12:51 ` Cornelia Huck
2018-02-08 8:30 ` Janosch Frank
2018-02-06 12:30 ` [PATCH 0/2] KVM: s390: avoid jump tables David Hildenbrand
2018-02-06 12:36 ` Christian Borntraeger
2018-02-06 12:42 ` David Hildenbrand
2018-02-08 8:58 ` Heiko Carstens [this message]
2018-02-08 9:07 ` Christian Borntraeger
2018-02-08 9:18 ` Christian Borntraeger
2018-02-08 10:09 ` Christian Borntraeger
2018-02-08 10:18 ` Cornelia Huck
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