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Tue, 20 May 2025 13:27:09 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3826.500.181.1.5\)) Subject: Re: [RFC v2 7/9] x86/mm: Introduce Remote Action Request From: Nadav Amit In-Reply-To: <6a3290319031cd68a383e416f53aa7549bac9407.camel@surriel.com> Date: Tue, 20 May 2025 23:26:57 +0300 Cc: Linux Kernel Mailing List , "open list:MEMORY MANAGEMENT" , the arch/x86 maintainers , kernel-team@meta.com, Dave Hansen , luto@kernel.org, peterz@infradead.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Yu-cheng Yu Content-Transfer-Encoding: quoted-printable Message-Id: <4009A0C6-CE5C-4197-9F48-3805059C214E@gmail.com> References: <20250520010350.1740223-1-riel@surriel.com> <20250520010350.1740223-8-riel@surriel.com> <4A879001-E213-4239-9D25-CDA8EC3E2CD9@gmail.com> <6a3290319031cd68a383e416f53aa7549bac9407.camel@surriel.com> To: Rik van Riel X-Mailer: Apple Mail (2.3826.500.181.1.5) X-Stat-Signature: nuhgyigeh51ffc5u5upaet7btybdnfnj X-Rspamd-Queue-Id: E917F40011 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1747772831-99524 X-HE-Meta: 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 JPTlt/Nz iL/uep3OPlpg770gd9ebNXa6S4a5BFQYTCQPEhqqzeAp45vOT6L4Ixl20PgEza0rnbDSCNh88JXLxIcOp5mkdkT8U/2sA7AttCUSRgX9wznOaO/jUpFxotB7bB4Uga9XnWQHpC0H1D/ktgGO3SOjAMTv58JhZWNjOW2eK4iGlfOWjy3dwH58CbyPdBUoL3RKx44GWc0MXfv94GcnL2VW2+QHG5ptP2813bsH3SelvCibvLJwW8GGurGPpTrdS9WiiE4EJmsqBwVRr+myPq75uoaLapzYvm1M1B64n4W2yJ1e5ojfmwkCG4oZBTNmMJE95P1TUVWvvLio9P7CieWJjyE4FIX4wFSpcJB3Pb9+oU2djPm30AzTZyN1k2VdriKWPcOjFaXdyS7YEfpCfRtoXbcPL3ja4um/fmHz3sMOuXe7iXpDJpXStfDaESP64qS60Chz9La8+jFUCmZBSPimdXyXT9iNqg4C2pltQ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On 20 May 2025, at 16:00, Rik van Riel wrote: >=20 >> Putting aside the rest of the code, I see you don=E2=80=99t call >> should_flush_tlb(). >> I think it is worth mentioning in commit log or comment the rationale >> behind >> it (and maybe benchmarks to justify it). >>=20 >>=20 > The long term plan here is to simply have the originating > CPU included in the cpumask, and have it send a RAR > request to itself. That=E2=80=99s unrelated. I was referring to considering supporting some sort of lazy TLB to eliminate sending RAR to cores that do not care about it. Is there a cost of RAR to more cores than needed? My guess is that there is one, and maybe in such cases you would want actual IPI and special handling.