From: Jon Masters <jcm@jonmasters.org> To: Will Deacon <will@kernel.org>, "qi.fuli@fujitsu.com" <qi.fuli@fujitsu.com> Cc: Jonathan Corbet <corbet@lwn.net>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Itaru Kitayama <itaru.kitayama@gmail.com>, "peterz@infradead.org" <peterz@infradead.org>, "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, "indou.takao@fujitsu.com" <indou.takao@fujitsu.com>, "maeda.naoaki@fujitsu.com" <maeda.naoaki@fujitsu.com>, "misono.tomohiro@fujitsu.com" <misono.tomohiro@fujitsu.com>, "tokamoto@jp.fujitsu.com" <tokamoto@jp.fujitsu.com> Subject: Re: [PATCH 0/2] arm64: Introduce boot parameter to disable TLB flush instruction within the same inner shareable domain Date: Sun, 1 Dec 2019 11:02:42 -0500 [thread overview] Message-ID: <a06ae400-29b2-d88f-af48-deafd7e355fe@jonmasters.org> (raw) In-Reply-To: <20191101172851.GC3983@willie-the-truck> On 11/1/19 1:28 PM, Will Deacon wrote: > On Fri, Nov 01, 2019 at 09:56:05AM +0000, qi.fuli@fujitsu.com wrote: >> In this thread, I explained that: >> * I found a performance problem which is caused by TLBI-is instruction. >> * The problem occurs like this: >> 1) On a core, OS tries to flush TLB using TLBI-is instruction >> 2) TLBI-is instruction causes a broadcast to all other cores, and >> each core received hard-wired signal >> 3) Each core check if there are TLB entries which have the specified >> ASID/VA (the above confuses implementation with architecture) <snip> > I think it's worth bearing in mind that I have little sympathy for the > problem that you are seeing. As far as I can tell, you've done the > following: > > 1. You designed a CPU micro-architecture that stalls whenever it receives > a TLB invalidation request. s/SPARC/Arm/ && wire in DVM > 2. You integrated said CPU design into a system where broadcast TLB > invalidation is not filtered and therefore stalls every CPU every > time that /any/ TLB invalidation is broadcast. > > 3. You deployed a mixture of Linux and jitter-sensitive software on > this system, and now you're failing to meet your performance > requirements. > > Have I got that right? > > If so, given that your CPU design isn't widely available, nobody else > appears to have made this mistake and jitter hasn't been reported as an > issue for any other systems, it's very unlikely that we're going to make > invasive upstream kernel changes to support you. I'm sorry, but all I can > suggest is that you check that your micro-architecture and performance > requirements are aligned with the design of Linux *before* building another > machine like this in future. > > I hate to be blunt, but I also don't want to waste your time. I always tried to ask nicely for the above to be heeded. There's a difference between "hi, our implementation doesn't scale, and here's why" vs "there's a problem with all TLBIs...". There isn't. The problem is the implementation and that should have been called out first thing. Jon. -- Computer Architect
WARNING: multiple messages have this Message-ID (diff)
From: Jon Masters <jcm@jonmasters.org> To: Will Deacon <will@kernel.org>, "qi.fuli@fujitsu.com" <qi.fuli@fujitsu.com> Cc: "tokamoto@jp.fujitsu.com" <tokamoto@jp.fujitsu.com>, "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>, "peterz@infradead.org" <peterz@infradead.org>, Catalin Marinas <catalin.marinas@arm.com>, Jonathan Corbet <corbet@lwn.net>, Will Deacon <will.deacon@arm.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "maeda.naoaki@fujitsu.com" <maeda.naoaki@fujitsu.com>, "misono.tomohiro@fujitsu.com" <misono.tomohiro@fujitsu.com>, Itaru Kitayama <itaru.kitayama@gmail.com>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, "indou.takao@fujitsu.com" <indou.takao@fujitsu.com> Subject: Re: [PATCH 0/2] arm64: Introduce boot parameter to disable TLB flush instruction within the same inner shareable domain Date: Sun, 1 Dec 2019 11:02:42 -0500 [thread overview] Message-ID: <a06ae400-29b2-d88f-af48-deafd7e355fe@jonmasters.org> (raw) In-Reply-To: <20191101172851.GC3983@willie-the-truck> On 11/1/19 1:28 PM, Will Deacon wrote: > On Fri, Nov 01, 2019 at 09:56:05AM +0000, qi.fuli@fujitsu.com wrote: >> In this thread, I explained that: >> * I found a performance problem which is caused by TLBI-is instruction. >> * The problem occurs like this: >> 1) On a core, OS tries to flush TLB using TLBI-is instruction >> 2) TLBI-is instruction causes a broadcast to all other cores, and >> each core received hard-wired signal >> 3) Each core check if there are TLB entries which have the specified >> ASID/VA (the above confuses implementation with architecture) <snip> > I think it's worth bearing in mind that I have little sympathy for the > problem that you are seeing. As far as I can tell, you've done the > following: > > 1. You designed a CPU micro-architecture that stalls whenever it receives > a TLB invalidation request. s/SPARC/Arm/ && wire in DVM > 2. You integrated said CPU design into a system where broadcast TLB > invalidation is not filtered and therefore stalls every CPU every > time that /any/ TLB invalidation is broadcast. > > 3. You deployed a mixture of Linux and jitter-sensitive software on > this system, and now you're failing to meet your performance > requirements. > > Have I got that right? > > If so, given that your CPU design isn't widely available, nobody else > appears to have made this mistake and jitter hasn't been reported as an > issue for any other systems, it's very unlikely that we're going to make > invasive upstream kernel changes to support you. I'm sorry, but all I can > suggest is that you check that your micro-architecture and performance > requirements are aligned with the design of Linux *before* building another > machine like this in future. > > I hate to be blunt, but I also don't want to waste your time. I always tried to ask nicely for the above to be heeded. There's a difference between "hi, our implementation doesn't scale, and here's why" vs "there's a problem with all TLBIs...". There isn't. The problem is the implementation and that should have been called out first thing. Jon. -- Computer Architect _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-12-01 19:17 UTC|newest] Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-06-17 14:32 [PATCH 0/2] arm64: Introduce boot parameter to disable TLB flush instruction within the same inner shareable domain Takao Indoh 2019-06-17 14:32 ` Takao Indoh 2019-06-17 14:32 ` [PATCH 1/2] arm64: mm: Restore mm_cpumask (revert commit 38d96287504a ("arm64: mm: kill mm_cpumask usage")) Takao Indoh 2019-06-17 14:32 ` Takao Indoh 2019-07-23 11:55 ` Catalin Marinas 2019-07-23 11:55 ` Catalin Marinas 2019-06-17 14:32 ` [PATCH 2/2] arm64: tlb: Add boot parameter to disable TLB flush within the same inner shareable domain Takao Indoh 2019-06-17 14:32 ` Takao Indoh 2019-07-23 12:11 ` Catalin Marinas 2019-07-23 12:11 ` Catalin Marinas 2019-06-17 17:03 ` [PATCH 0/2] arm64: Introduce boot parameter to disable TLB flush instruction " Will Deacon 2019-06-17 17:03 ` Will Deacon 2019-06-24 10:34 ` qi.fuli 2019-06-24 10:34 ` qi.fuli 2019-06-27 10:27 ` Will Deacon 2019-06-27 10:27 ` Will Deacon 2019-07-03 2:45 ` qi.fuli 2019-07-03 2:45 ` qi.fuli 2019-07-09 0:25 ` Jon Masters 2019-07-09 0:25 ` Jon Masters 2019-07-09 0:29 ` Jon Masters 2019-07-09 0:29 ` Jon Masters 2019-07-09 8:03 ` Will Deacon 2019-07-09 8:03 ` Will Deacon 2019-07-09 8:07 ` Will Deacon 2019-07-09 8:07 ` Will Deacon 2019-11-01 9:56 ` qi.fuli 2019-11-01 9:56 ` qi.fuli 2019-11-01 17:28 ` Will Deacon 2019-11-01 17:28 ` Will Deacon 2019-11-26 14:26 ` Matthias Brugger 2019-11-26 14:26 ` Matthias Brugger 2019-11-26 14:36 ` Will Deacon 2019-11-26 14:36 ` Will Deacon 2019-12-01 16:02 ` Jon Masters [this message] 2019-12-01 16:02 ` Jon Masters
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