From: "Philippe Mathieu-Daudé" <philmd@linaro.org>
To: "Ani Sinha" <anisinha@redhat.com>,
"Daniel P. Berrangé" <berrange@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Richard Henderson <richard.henderson@linaro.org>,
Eduardo Habkost <eduardo@habkost.net>,
"Michael S. Tsirkin" <mst@redhat.com>,
Marcel Apfelbaum <marcel.apfelbaum@gmail.com>,
Igor Mammedov <imammedo@redhat.com>,
Julia Suvorova <jusual@redhat.com>,
QEMU Developers <qemu-devel@nongnu.org>,
Gerd Hoffmann <kraxel@redhat.com>
Subject: Re: [PATCH] pc: q35: Bump max_cpus to 1728 vcpus
Date: Tue, 30 Jan 2024 20:07:25 +0100 [thread overview]
Message-ID: <694417c4-b976-47f7-bc61-a84a48ead117@linaro.org> (raw)
In-Reply-To: <4CEF526A-5B22-41EA-8634-D4BB5871B739@redhat.com>
On 30/1/24 18:09, Ani Sinha wrote:
>
>
>> On 30-Jan-2024, at 22:17, Daniel P. Berrangé <berrange@redhat.com> wrote:
>>
>> On Tue, Jan 30, 2024 at 10:14:28PM +0530, Ani Sinha wrote:
>>> Since commit f10a570b093e6 ("KVM: x86: Add CONFIG_KVM_MAX_NR_VCPUS to allow up to 4096 vCPUs")
>>> Linux kernel can support upto a maximum number of 4096 vCPUS when MAXSMP is
>>> enabled in the kernel. QEMU has been tested to correctly boot a linux guest
>>> with 1728 vcpus both with edk2 and seabios firmwares. So bump up the max_cpus
>>> value for q35 machines versions 9 and newer to 1728. Q35 machines versions
>>> 8.2 and older continue to support 1024 maximum vcpus as before for
>>> compatibility.
>>
>> Where does the 1728 number come from ?
>>
>> Did something break at 1729, or did the test machine simply not
>> have sufficient resources to do practical larger tests ?
>
> Actual limit currently is 1856 for EDK2. The HPE folks tested QEMU with edk2 and QEMU fails to boot beyond that limit.
> There are RH internal bugs tracking this and Gerd is working on it from RH side [1].
>
> We would ultimately like to go to 8192 vcpus for SAP HANA but 1728 vcpus is our immediate target for now. If you want, I can resend the patch with 1856 since that is currently the tested limit.
>
> 1. https://issues.redhat.com/browse/RHEL-22202
Out of curiosity has the limit to be multiple of 64?
next prev parent reply other threads:[~2024-01-30 19:07 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-30 16:44 [PATCH] pc: q35: Bump max_cpus to 1728 vcpus Ani Sinha
2024-01-30 16:47 ` Daniel P. Berrangé
2024-01-30 17:09 ` Ani Sinha
2024-01-30 17:13 ` Daniel P. Berrangé
2024-01-30 19:07 ` Philippe Mathieu-Daudé [this message]
2024-01-30 22:17 ` Michael S. Tsirkin
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