From: marc.zyngier@arm•com (Marc Zyngier)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v2 00/21] arm64: KVM: world switch in C
Date: Tue, 01 Dec 2015 09:58:23 +0000 [thread overview]
Message-ID: <565D6F3F.5030700@arm.com> (raw)
In-Reply-To: <20151130203345.GI11704@cbox>
On 30/11/15 20:33, Christoffer Dall wrote:
> On Fri, Nov 27, 2015 at 06:49:54PM +0000, Marc Zyngier wrote:
>> Once upon a time, the KVM/arm64 world switch was a nice, clean, lean
>> and mean piece of hand-crafted assembly code. Over time, features have
>> crept in, the code has become harder to maintain, and the smallest
>> change is a pain to introduce. The VHE patches are a prime example of
>> why this doesn't work anymore.
>>
>> This series rewrites most of the existing assembly code in C, but keeps
>> the existing code structure in place (most function names will look
>> familiar to the reader). The biggest change is that we don't have to
>> deal with a static register allocation (the compiler does it for us),
>> we can easily follow structure and pointers, and only the lowest level
>> is still in assembly code. Oh, and a negative diffstat.
>>
>> There is still a healthy dose of inline assembly (system register
>> accessors, runtime code patching), but I've tried not to make it too
>> invasive. The generated code, while not exactly brilliant, doesn't
>> look too shaby. I do expect a small performance degradation, but I
>> believe this is something we can improve over time (my initial
>> measurements don't show any obvious regression though).
>
> I ran this through my experimental setup on m400 and got this:
[...]
> What this tells me is that we do take a noticable hit on the
> world-switch path, which shows up in the TCP_RR and hackbench workloads,
> which have a high precision in their output.
>
> Note that the memcached number is well within its variability between
> individual benchmark runs, where it varies to 12% of its average in over
> 80% of the executions.
>
> I don't think this is a showstopper thought, but we could consider
> looking more closely at a breakdown of the world-switch path and verify
> if/where we are really taking a hit.
Thanks for doing so, very interesting. As a data point, what compiler
are you using? I'd expect some variability based on the compiler version...
Thanks,
M.
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2015-12-01 9:58 UTC|newest]
Thread overview: 88+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-27 18:49 [PATCH v2 00/21] arm64: KVM: world switch in C Marc Zyngier
2015-11-27 18:49 ` [PATCH v2 01/21] arm64: Add macros to read/write system registers Marc Zyngier
2015-11-30 20:00 ` Christoffer Dall
2015-11-27 18:49 ` [PATCH v2 02/21] arm64: KVM: Add a HYP-specific header file Marc Zyngier
2015-11-30 20:00 ` Christoffer Dall
2015-12-01 11:41 ` Marc Zyngier
2015-12-01 11:47 ` Christoffer Dall
2015-11-27 18:49 ` [PATCH v2 03/21] arm64: KVM: Implement vgic-v2 save/restore Marc Zyngier
2015-11-30 20:00 ` Christoffer Dall
2015-12-01 11:39 ` Marc Zyngier
2015-11-27 18:49 ` [PATCH v2 04/21] arm64: KVM: Implement vgic-v3 save/restore Marc Zyngier
2015-11-30 9:59 ` Alex Bennée
2015-11-30 10:43 ` Marc Zyngier
2015-11-30 19:50 ` Christoffer Dall
2015-12-01 11:32 ` Marc Zyngier
2015-12-01 11:44 ` Christoffer Dall
2015-12-01 11:50 ` Christoffer Dall
2015-12-01 11:57 ` Marc Zyngier
2015-12-01 12:24 ` Christoffer Dall
2015-12-01 12:49 ` Marc Zyngier
2015-12-01 11:54 ` Marc Zyngier
2015-11-27 18:49 ` [PATCH v2 05/21] arm64: KVM: Implement timer save/restore Marc Zyngier
2015-11-30 19:59 ` Christoffer Dall
2015-12-01 11:34 ` Marc Zyngier
2015-11-27 18:50 ` [PATCH v2 06/21] arm64: KVM: Implement system register save/restore Marc Zyngier
2015-12-01 15:53 ` Christoffer Dall
2015-11-27 18:50 ` [PATCH v2 07/21] arm64: KVM: Implement 32bit " Marc Zyngier
2015-12-01 15:52 ` Christoffer Dall
2015-11-27 18:50 ` [PATCH v2 08/21] arm64: KVM: Implement debug save/restore Marc Zyngier
2015-11-30 12:00 ` Alex Bennée
2015-11-30 12:24 ` Marc Zyngier
2015-12-01 12:56 ` Christoffer Dall
2015-12-01 13:06 ` Marc Zyngier
2015-12-01 13:19 ` Alex Bennée
2015-12-01 13:34 ` Marc Zyngier
2015-12-01 14:47 ` Christoffer Dall
2015-12-01 14:56 ` Christoffer Dall
2015-12-01 15:01 ` Marc Zyngier
2015-12-01 15:41 ` Christoffer Dall
2015-12-01 18:34 ` Marc Zyngier
2015-11-27 18:50 ` [PATCH v2 09/21] arm64: KVM: Implement guest entry Marc Zyngier
2015-12-01 15:29 ` Christoffer Dall
2015-12-01 18:41 ` Marc Zyngier
2015-11-27 18:50 ` [PATCH v2 10/21] arm64: KVM: Add patchable function selector Marc Zyngier
2015-12-01 15:39 ` Christoffer Dall
2015-12-01 18:51 ` Marc Zyngier
2015-12-02 9:27 ` Christoffer Dall
2015-12-02 9:47 ` Marc Zyngier
2015-12-02 11:53 ` Christoffer Dall
2015-12-02 13:19 ` Marc Zyngier
2015-12-02 16:19 ` Christoffer Dall
2015-12-02 22:34 ` Andrew Jones
2015-12-03 8:18 ` Marc Zyngier
2015-11-27 18:50 ` [PATCH v2 11/21] arm64: KVM: Implement the core world switch Marc Zyngier
2015-12-01 15:55 ` Christoffer Dall
2015-11-27 18:50 ` [PATCH v2 12/21] arm64: KVM: Implement fpsimd save/restore Marc Zyngier
2015-12-02 11:53 ` Christoffer Dall
2015-12-02 15:29 ` Marc Zyngier
2015-12-02 16:19 ` Christoffer Dall
2015-11-27 18:50 ` [PATCH v2 13/21] arm64: KVM: Implement TLB handling Marc Zyngier
2015-12-02 11:53 ` Christoffer Dall
2015-11-27 18:50 ` [PATCH v2 14/21] arm64: KVM: HYP mode entry points Marc Zyngier
2015-12-02 11:53 ` Christoffer Dall
2015-11-27 18:50 ` [PATCH v2 15/21] arm64: KVM: Add panic handling Marc Zyngier
2015-12-02 11:53 ` Christoffer Dall
2015-11-27 18:50 ` [PATCH v2 16/21] arm64: KVM: Add compatibility aliases Marc Zyngier
2015-12-02 11:49 ` Christoffer Dall
2015-12-02 15:23 ` Marc Zyngier
2015-11-27 18:50 ` [PATCH v2 17/21] arm64: KVM: Map the kernel RO section into HYP Marc Zyngier
2015-12-02 11:49 ` Christoffer Dall
2015-11-27 18:50 ` [PATCH v2 18/21] arm64: KVM: Move away from the assembly version of the world switch Marc Zyngier
2015-12-02 11:49 ` Christoffer Dall
2015-11-27 18:50 ` [PATCH v2 19/21] arm64: KVM: Turn system register numbers to an enum Marc Zyngier
2015-12-02 11:51 ` Christoffer Dall
2015-12-02 15:26 ` Marc Zyngier
2015-11-27 18:50 ` [PATCH v2 20/21] arm64: KVM: Cleanup asm-offset.c Marc Zyngier
2015-12-02 11:51 ` Christoffer Dall
2015-11-27 18:50 ` [PATCH v2 21/21] arm64: KVM: Remove weak attributes Marc Zyngier
2015-12-02 11:47 ` Christoffer Dall
2015-12-02 15:21 ` Marc Zyngier
2015-12-02 16:21 ` Christoffer Dall
2015-12-02 17:52 ` Marc Zyngier
2015-11-30 20:33 ` [PATCH v2 00/21] arm64: KVM: world switch in C Christoffer Dall
2015-12-01 3:19 ` Mario Smarduch
2015-12-01 9:58 ` Marc Zyngier [this message]
2015-12-01 12:00 ` Christoffer Dall
2015-12-01 17:51 ` Marc Zyngier
2015-12-01 19:34 ` Christoffer Dall
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