From: Nadav Amit <nadav.amit@gmail.com>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: "Sean Christopherson" <sean.j.christopherson@intel.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>,
"Paolo Bonzini" <pbonzini@redhat.com>
Subject: Re: [PATCH v3 0/3] KVM: Yield to IPI target if necessary
Date: Tue, 11 Jun 2019 18:37:36 -0700 [thread overview]
Message-ID: <28BF5471-57E8-41FE-B401-D49D57D01A63@gmail.com> (raw)
In-Reply-To: <CANRm+Cx6Z=jxLaXqwhBDpVTsKH8mgoo4iC=U8GbAAJz-5gk5ZA@mail.gmail.com>
> On Jun 11, 2019, at 6:18 PM, Wanpeng Li <kernellwp@gmail.com> wrote:
>
> On Wed, 12 Jun 2019 at 00:57, Nadav Amit <nadav.amit@gmail.com> wrote:
>>> On Jun 11, 2019, at 3:02 AM, Wanpeng Li <kernellwp@gmail.com> wrote:
>>>
>>> On Tue, 11 Jun 2019 at 09:48, Nadav Amit <nadav.amit@gmail.com> wrote:
>>>>> On Jun 10, 2019, at 6:45 PM, Wanpeng Li <kernellwp@gmail.com> wrote:
>>>>>
>>>>> On Tue, 11 Jun 2019 at 09:11, Sean Christopherson
>>>>> <sean.j.christopherson@intel.com> wrote:
>>>>>> On Mon, Jun 10, 2019 at 04:34:20PM +0200, Radim Krčmář wrote:
>>>>>>> 2019-05-30 09:05+0800, Wanpeng Li:
>>>>>>>> The idea is from Xen, when sending a call-function IPI-many to vCPUs,
>>>>>>>> yield if any of the IPI target vCPUs was preempted. 17% performance
>>>>>>>> increasement of ebizzy benchmark can be observed in an over-subscribe
>>>>>>>> environment. (w/ kvm-pv-tlb disabled, testing TLB flush call-function
>>>>>>>> IPI-many since call-function is not easy to be trigged by userspace
>>>>>>>> workload).
>>>>>>>
>>>>>>> Have you checked if we could gain performance by having the yield as an
>>>>>>> extension to our PV IPI call?
>>>>>>>
>>>>>>> It would allow us to skip the VM entry/exit overhead on the caller.
>>>>>>> (The benefit of that might be negligible and it also poses a
>>>>>>> complication when splitting the target mask into several PV IPI
>>>>>>> hypercalls.)
>>>>>>
>>>>>> Tangetially related to splitting PV IPI hypercalls, are there any major
>>>>>> hurdles to supporting shorthand? Not having to generate the mask for
>>>>>> ->send_IPI_allbutself and ->kvm_send_ipi_all seems like an easy to way
>>>>>> shave cycles for affected flows.
>>>>>
>>>>> Not sure why shorthand is not used for native x2apic mode.
>>>>
>>>> Why do you say so? native_send_call_func_ipi() checks if allbutself
>>>> shorthand should be used and does so (even though the check can be more
>>>> efficient - I’m looking at that code right now…)
>>>
>>> Please continue to follow the apic/x2apic driver. Just apic_flat set
>>> APIC_DEST_ALLBUT/APIC_DEST_ALLINC to ICR.
>>
>> Indeed - I was sure by the name that it does it correctly. That’s stupid.
>>
>> I’ll add it to the patch-set I am working on (TLB shootdown improvements),
>> if you don’t mind.
>
> Original for hotplug cpu safe.
> https://lwn.net/Articles/138365/
> https://lwn.net/Articles/138368/
> Not sure shortcut native support is acceptable, I will play my
> kvm_send_ipi_allbutself and kvm_send_ipi_all. :)
Yes, I saw these threads before. But I think the test in
native_send_call_func_ipi() should take care of it.
I’ll recheck.
next prev parent reply other threads:[~2019-06-12 1:37 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-30 1:05 [PATCH v3 0/3] KVM: Yield to IPI target if necessary Wanpeng Li
2019-05-30 1:05 ` [PATCH v3 1/3] KVM: X86: " Wanpeng Li
2019-05-30 1:05 ` [PATCH v3 2/3] KVM: X86: Implement PV sched yield hypercall Wanpeng Li
2019-06-10 14:17 ` Radim Krčmář
2019-06-11 8:47 ` Wanpeng Li
2019-05-30 1:05 ` [PATCH v3 3/3] KVM: X86: Expose PV_SCHED_YIELD CPUID feature bit to guest Wanpeng Li
2019-06-10 5:58 ` [PATCH v3 0/3] KVM: Yield to IPI target if necessary Wanpeng Li
2019-06-10 14:34 ` Radim Krčmář
2019-06-11 1:11 ` Sean Christopherson
2019-06-11 1:45 ` Wanpeng Li
2019-06-11 1:48 ` Nadav Amit
2019-06-11 10:02 ` Wanpeng Li
2019-06-11 16:57 ` Nadav Amit
2019-06-12 1:18 ` Wanpeng Li
2019-06-12 1:37 ` Nadav Amit [this message]
2019-06-28 9:12 ` Wanpeng Li
2019-06-28 9:18 ` Wanpeng Li
2019-06-11 10:26 ` Wanpeng Li
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=28BF5471-57E8-41FE-B401-D49D57D01A63@gmail.com \
--to=nadav.amit@gmail.com \
--cc=kernellwp@gmail.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=pbonzini@redhat.com \
--cc=rkrcmar@redhat.com \
--cc=sean.j.christopherson@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).