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Tue, 05 Nov 2019 02:23:19 -0800 (PST) X-Google-Smtp-Source: APXvYqzBZkub82r+YaidAWnAVsPcUzN7WWqgOtKY4bu/OLSPh9FFpp+MoOYAmoKCvjjxybqwhQOC/A== X-Received: by 2002:a05:600c:214b:: with SMTP id v11mr3615883wml.149.1572949399478; Tue, 05 Nov 2019 02:23:19 -0800 (PST) Received: from [192.168.10.150] ([93.56.166.5]) by smtp.gmail.com with ESMTPSA id w9sm21506531wrt.85.2019.11.05.02.23.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 05 Nov 2019 02:23:18 -0800 (PST) Subject: Re: [PATCH 13/13] x86: retpolines: eliminate retpoline from msr event handlers To: Andrea Arcangeli , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Vitaly Kuznetsov , Sean Christopherson References: <20191104230001.27774-1-aarcange@redhat.com> <20191104230001.27774-14-aarcange@redhat.com> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: <306784c2-25b0-9f25-c9e0-c23aaee11e4f@redhat.com> Date: Tue, 5 Nov 2019 11:21:08 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20191104230001.27774-14-aarcange@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/11/19 00:00, Andrea Arcangeli wrote: > It's enough to check the value and issue the direct call. > > After this commit is applied, here the most common retpolines executed > under a high resolution timer workload in the guest on a VMX host: > > [..] > @[ > trace_retpoline+1 > __trace_retpoline+30 > __x86_indirect_thunk_rax+33 > do_syscall_64+89 > entry_SYSCALL_64_after_hwframe+68 > ]: 267 > @[]: 2256 > @[ > trace_retpoline+1 > __trace_retpoline+30 > __x86_indirect_thunk_rax+33 > __kvm_wait_lapic_expire+284 > vmx_vcpu_run.part.97+1091 > vcpu_enter_guest+377 > kvm_arch_vcpu_ioctl_run+261 > kvm_vcpu_ioctl+559 > do_vfs_ioctl+164 > ksys_ioctl+96 > __x64_sys_ioctl+22 > do_syscall_64+89 > entry_SYSCALL_64_after_hwframe+68 > ]: 2390 > @[]: 33410 > > @total: 315707 > > Note the highest hit above is __delay so probably not worth optimizing > even if it would be more frequent than 2k hits per sec. > > Signed-off-by: Andrea Arcangeli > --- > arch/x86/events/intel/core.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c > index fcef678c3423..937363b803c1 100644 > --- a/arch/x86/events/intel/core.c > +++ b/arch/x86/events/intel/core.c > @@ -3323,8 +3323,19 @@ static int intel_pmu_hw_config(struct perf_event *event) > return 0; > } > > +#ifdef CONFIG_RETPOLINE > +static struct perf_guest_switch_msr *core_guest_get_msrs(int *nr); > +static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr); > +#endif > + > struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr) > { > +#ifdef CONFIG_RETPOLINE > + if (x86_pmu.guest_get_msrs == intel_guest_get_msrs) > + return intel_guest_get_msrs(nr); > + else if (x86_pmu.guest_get_msrs == core_guest_get_msrs) > + return core_guest_get_msrs(nr); > +#endif > if (x86_pmu.guest_get_msrs) > return x86_pmu.guest_get_msrs(nr); > *nr = 0; > Queued, thanks. Paolo