From: Christian Borntraeger <borntraeger@de.ibm.com>
To: Heiko Carstens <heiko.carstens@de.ibm.com>,
David Hildenbrand <david@redhat.com>
Cc: 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 10:07:40 +0100 [thread overview]
Message-ID: <1cce9ec4-d32e-a12b-7151-f719cd68f72e@de.ibm.com> (raw)
In-Reply-To: <20180208085819.GC3937@osiris>
On 02/08/2018 09:58 AM, Heiko Carstens wrote:
> 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.
Seems to depend on the compiler. The gcc 7.2 from my Fedora 27 seems to do
the right thing for intercept.o and priv.o.
In the end this will also help the new -mindirect-branch thing as the gcc
support also avoids jump tables if we use thunks.
next prev parent reply other threads:[~2018-02-08 9:07 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
2018-02-08 9:07 ` Christian Borntraeger [this message]
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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