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a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1678652725; bh=bnupbG1JXCaGHSBZxVm2cva37si3CwmVtUwbAWr6WcI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=iDLPl4h5XIb8/AG1ekwgzeXNJXNk2wwFSl8bRTJLND9d3EZq7wq4/QZIM/9knXxI0 otS3kmfH1sioquSHmNJ4+IKrf81DSv8KOuPeBXVf5efXBvYm1D17+qsiw/e1+tzCfP FjYowqM3AKzXuAMME2W6lLAWhENstmSOjM9ecf9o= Date: Sun, 12 Mar 2023 13:25:24 -0700 From: Andrew Morton To: Yair Podemsky Cc: will@kernel.org, aneesh.kumar@linux.ibm.com, npiggin@gmail.com, peterz@infradead.org, arnd@arndb.de, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, mtosatti@redhat.com, ppandit@redhat.com, alougovs@redhat.com, David Hildenbrand Subject: Re: [PATCH] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to MM CPUs Message-Id: <20230312132524.c37abfffe2c70eeda20f3217@linux-foundation.org> In-Reply-To: <20230312080945.14171-1-ypodemsk@redhat.com> References: <20230312080945.14171-1-ypodemsk@redhat.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: E48751C0016 X-Rspamd-Server: rspam01 X-Stat-Signature: pa69kedbdjqneh3mp3fg33yxaqupu3fm X-HE-Tag: 1678652726-588672 X-HE-Meta: U2FsdGVkX18CVJFo0ugHmekF6Q4UIQ+rHBtMG0YhHT8d37LpkKcp8R248Rx/SafThYsEU3lIIlZNmmMV1DHGJH0XBeuA5zg/NZPgoFcKsp6dCJ6+BxdmnOm7DcE2zIfUpVX8f+22nt1t1bLRDNU9vAvvWoLoI+iKLTma1pox2tdeNo2DwUILAEmqY684bIzMeQaTMfOJGP6xjzmtJPi0P7zOeLPfzZmL1ntF97bjkF4O8JdNUaA0dVI+a15kPeP5cFPmkQU6fMz8mKfsh6cb8ZA09/5sDSG0pOU68sA84ZyXa2NgysqQfqsilgFIzNzSfOkzGVkMsq4gWzs3XMSik2d3DqYuAWTiIYrIkdAVuMwn8Rpw3byJNICUauWybnTijq26181u8jAFaY5h0Gb3BnOlUDaTZNnFzZKG2UHp2Ztc1KONEEw1VerNlSXHNENRd4y/9LcUaEeU+fSshzSFl/OHW4Gt/4Nct273AXQih5B0hurMg20QIbejd1506veC34TryPqgiyc4tEvr5VdDwQlYNfszzAe7GmS9USIctJOygQhVImf1LgWxvgoww9LTl/EUTr6XXOQ9H1ZRCR3RzZ+Z2GUPdSNCiJHO9y1RZc5xPzecN3ibaIVQbfhYSmmlLk+Sig83hVaR/rnSRkCXxNT76DrK8Q55EM5il4A9WBS8+yr65wqfkJRUUyNhFZ7IBGUtNocq0X893XeHKgIwIWid/KKYP8f8zQc7Y8MxBmHqPZ++5BWCBb3YIGE6YmkywYH5FsRgvF2K27mDj8tI9ShHAZTcA4wk4ulWJIW3tHcaWR5brEBvHx3/Ixw46uxSx/2SNsXYX9uZF3pIY/Symp31I/6l53juHI64gJ+htRxiXLHL5cqgVbfHOFEVL03Yi+I2CB+n/wpj884ghnyprB1+LSzvLv7TJx6xbCCLFo/Di9H1phSHGWEB9cMcC8C/Nsvhvga6gvL+ABi4umE BHdTKOlE cN4ZHifxIUnkpwGojR7LqTkJkCip5BCIvNPEG4z62SSEdmFFQ+VwgZ6SP/shqjEB/s6HVN5+La66hGaqN1OURJJY/H1a3o+Z8+uQnp/CnaJnXPB7QkrRbyGYIaVthJyPnqi33rXc0wEWY9JJdcnD4yheF812HmhBCECLDYj6ZSemdlmJwfGh1gs+qBCoUpRo7SM44iMD/wVuEo81RvWtvmVxkKN1xYddRQ9WwQVzzoccC3+XwRk4YW7r7MMyOb/bQ2XFNE1cpWublKNopNFQpeEjSFqNX92fNjHGapAjJ4HQtvgPUK6jLOU2yEGeV8cLYLMeN85PH9HdB7IDVOD2likb1Sh6Cr6nGUEm9ewX7b/+Om61TUynFl5mkat8UmedIPIWak5onyZX23nyMnmV9MnYktCxAGRfrfZpS 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: On Sun, 12 Mar 2023 10:09:45 +0200 Yair Podemsky wrote: > Currently the tlb_remove_table_smp_sync IPI is sent to all CPUs > indiscriminately, this causes unnecessary work and delays notable in > real-time use-cases and isolated cpus, this patch will limit this IPI to > only be sent to cpus referencing the effected mm and are currently in > kernel space. > > ... > > --- a/mm/mmu_gather.c > +++ b/mm/mmu_gather.c > @@ -191,7 +192,15 @@ static void tlb_remove_table_smp_sync(void *arg) > /* Simply deliver the interrupt */ > } > > -void tlb_remove_table_sync_one(void) > +static bool cpu_in_kernel(int cpu, void *info) > +{ > + struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu); > + int statue = atomic_read(&ct->state); Strange identifier. Should be "state"? > + //will return true only for cpu's in kernel space Please use /* */ style comments And use "cpus" rather than "cpu's" - plural, not possessive. > + return !(statue & CT_STATE_MASK); Using return state & CT_STATE_MASK == CONTEXT_KERNEL; would more clearly express the intent. > +} And... surely this function is racy. ct->state can change value one nanosecond after cpu_in_kernel() reads it, so cpu_in_kernel()'s return value is now wrong?