From: Sean Christopherson <seanjc@google.com>
To: Isaku Yamahata <isaku.yamahata@intel.com>
Cc: kvm@vger.kernel.org, isaku.yamahata@gmail.com,
Paolo Bonzini <pbonzini@redhat.com>,
isaku.yamahata@linux.intel.com
Subject: Re: [kvm-unit-tests PATCH] x86: apic, vmexit: replace nop with serialize to wait for deadline timer
Date: Wed, 4 Feb 2026 06:21:48 -0800 [thread overview]
Message-ID: <aYNV_KJc6WDo0_cH@google.com> (raw)
In-Reply-To: <aYJFdgUxYWXkavfi@iyamahat-desk>
On Tue, Feb 03, 2026, Isaku Yamahata wrote:
> On Tue, Feb 03, 2026 at 10:30:06AM -0800,
> Sean Christopherson <seanjc@google.com> wrote:
>
> > > +static inline void serialize(void)
> > > +{
> > > + /* serialize instruction. It needs binutils >= 2.35. */
> >
> > And a CPU that supports it... I don't see any point in using SERIALIZE. To check
> > for support, this code would need to do CPUID to query X86_FEATURE_SERIALIZE, and
> > CPUID itself is serializing (the big reason to favor SERIALIZE over CPUID is to
> > avoid a VM-Exit for performance reasons).
>
> Thank you for pointing it out. I'll replace it with raw_cpuid(0, 0).
> Or do you want to opencode cpuid() in each places?
It probably makes sense to add a helper to arm the deadline timer, and deal with
the serialization there. E.g. start_tsc_deadline_timer() also has a nop() of
dubious value.
prev parent reply other threads:[~2026-02-04 14:21 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-03 18:20 [kvm-unit-tests PATCH] x86: apic, vmexit: replace nop with serialize to wait for deadline timer isaku.yamahata
2026-02-03 18:30 ` Sean Christopherson
2026-02-03 18:59 ` Isaku Yamahata
2026-02-04 14:21 ` Sean Christopherson [this message]
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=aYNV_KJc6WDo0_cH@google.com \
--to=seanjc@google.com \
--cc=isaku.yamahata@gmail.com \
--cc=isaku.yamahata@intel.com \
--cc=isaku.yamahata@linux.intel.com \
--cc=kvm@vger.kernel.org \
--cc=pbonzini@redhat.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