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AJvYcCXdjpd+F/lqhRzpH9Pr0ch8uW3nzw7p9KwqQWN/C7WWCq3C7e2HKyrDqjNdgD2wyrTnKlL0Irdwq1kaZLs=@vger.kernel.org X-Gm-Message-State: AOJu0YxRqBSn6IrSeSXcITRGqsSGJgMUHx3RYbT5tgpEaeiIeeWYX0p3 kRP9dimD/RAcek33h2vEa10yekoH4IBSxD1x5/IkcNO0rMbo68BMbk8lpSd4G2SB23jUKR6izUV lLB01ug== X-Received: from pga25.prod.google.com ([2002:a05:6a02:4f99:b0:c08:9db4:d5d2]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:939d:b0:35f:84c7:4012 with SMTP id adf61e73a8af0-39447379f56mr21025637.29.1770828548500; Wed, 11 Feb 2026 08:49:08 -0800 (PST) Date: Wed, 11 Feb 2026 08:49:06 -0800 In-Reply-To: <18c8bccc-f57f-401c-9b86-248d1632f9d9@citrix.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260211102928.100944-1-ubizjak@gmail.com> <2af5e3a8-f520-40fd-96a5-28555c3e4a5e@citrix.com> <20260211134342.45b7e19e@pumpkin> <5276256b-9669-46df-8fcd-b216f3d3e45b@citrix.com> <18c8bccc-f57f-401c-9b86-248d1632f9d9@citrix.com> Message-ID: Subject: Re: [PATCH 1/2] KVM: VMX: Drop obsolete branch hint prefixes from inline asm From: Sean Christopherson To: Andrew Cooper Cc: David Laight , ubizjak@gmail.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@kernel.org, pbonzini@redhat.com, tglx@kernel.org, x86@kernel.org Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Wed, Feb 11, 2026, Andrew Cooper wrote: > On 11/02/2026 4:17 pm, Sean Christopherson wrote: > > On Wed, Feb 11, 2026, Andrew Cooper wrote: > >> On 11/02/2026 3:44 pm, Sean Christopherson wrote: > >>> On Wed, Feb 11, 2026, Andrew Cooper wrote: > >> This change is almost certainly marginal at best.=C2=A0 It's not as if > >> VMREAD/VMWRITE lead to good code gen even at the best of times. > > Yeah, but adding in them in the first place was even more marginal (I a= dded the > > hints as much for documentation purposes as anything else). Absent pro= of that > > having the hints is a net positive, I'm inclined to trust the compiler = folks on > > what is/isn't optimal, and drop them. >=20 > Branch mispredicts in the P4 could easily eat up 150 cycles before the > frontend got it's act together. Heh, I'm willing to risk getting yelled at by the one person running KVM on= P4. > However, optimising VMREAD/VMWRITE and not the whole kernel seems > somewhat futile. >=20 > ~Andrew