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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=BPF300yctVWoLPyajY/1eckOE/YPyOmy73M8lcze7widDDtFsyVEEAA9T55Op/ncD bhdVuIouPtzCVpbex3DajbZqolsIGgogwFuIV59IakOpDzCHf61il3tCGTjCnMOxba NQRu5+qgd4RT0a0hjSz9uWDrmPtHoBKueR3fAJWbjE0iC04O6ogIfeRbixtxipR2pT 5Y/Rf1EYtttg/sI7tBkpH1Iwm3ZNHm5Br8JaC37o1a0c2SWyVlzTAUqov5xX6Mkrbj F8yCB6ja+JO1GgcEhM9NvbesIveOtCXuLcDVTWpZuI5JKoNeFB4l22ksS4s5krIK+P KYkL8rbH+lzHg== Message-ID: <449bd407-0f54-47dc-bb3c-034e92a5145b@zytor.com> Date: Wed, 12 Feb 2025 00:33:06 -0800 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 10/23] x86/resctrl: Remove MSR reading of event configuration value To: babu.moger@amd.com, Reinette Chatre , corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, tony.luck@intel.com, peternewman@google.com Cc: x86@kernel.org, hpa@zytor.com, paulmck@kernel.org, akpm@linux-foundation.org, thuth@redhat.com, rostedt@goodmis.org, xiongwei.song@windriver.com, pawan.kumar.gupta@linux.intel.com, daniel.sneddon@linux.intel.com, jpoimboe@kernel.org, perry.yuan@amd.com, sandipan.das@amd.com, kai.huang@intel.com, xiaoyao.li@intel.com, seanjc@google.com, xin3.li@intel.com, andrew.cooper3@citrix.com, ebiggers@google.com, mario.limonciello@amd.com, james.morse@arm.com, tan.shaopeng@fujitsu.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, maciej.wieczor-retman@intel.com, eranian@google.com References: <0fc8dbd4-07d8-40bd-8eec-402b48762807@zytor.com> Content-Language: en-US From: Xin Li Autocrypt: addr=xin@zytor.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2/11/2025 11:44 AM, Moger, Babu wrote: > Hi Xin, > > On 2/7/25 04:07, Xin Li wrote: >> On 2/6/2025 8:17 AM, Reinette Chatre wrote: >>>>> +    wrmsr(MSR_IA32_EVT_CFG_BASE + index, mon_info->mon_config, 0); >>>> This is the existing code, however it would be better to use wrmsrl() >>>> when the higher 32-bit are all 0s: >>>> >>>>      wrmsrl(MSR_IA32_EVT_CFG_BASE + index, mon_info->mon_config); >>>> >>> Could you please elaborate what makes this change better? >> >> In short, it takes one less argument, and doesn't pass an argument of 0. >> >> The longer story is that hpa and I are refactoring the MSR access APIs >> to accommodate the immediate form of MSR access instructions.  And we >> are not happy about that there are too many MSR access APIs and their >> uses are *random*.  The native wrmsr() and wrmsrl() are essentially the >> same and the only difference is that wrmsr() passes a 64-bit value to be >> written into a MSR in *2* u32 arguments.  But we already have struct msr >> defined in asm/shared/msr.h as: >>     struct msr { >>             union { >>                     struct { >>                             u32 l; >>                             u32 h; >>                     }; >>                     u64 q; >>             }; >>     }; >> >> it's more natural to do the same job with this data structure in most >> cases.  And we want to remove wrmsr() and only keep wrmsrl(), thus a >> developer won't have to figure out which one is better to use :-P. >> >> For that to happen, one cleanup is to replace wrmsr(msr, low, 0) with >> wrmsrl(msr, low) (low is automatically converted to u64 from u32). >> >> However, I'm fine if Babu wants to keep it as-is. > > Thanks for the explanation. Changed it to use wrmsrl(). > You're welcome. And thanks for making the change.