From mboxrd@z Thu Jan 1 00:00:00 1970 From: Borislav Petkov Subject: Re: [PATCH v2 3/3] x86/mm: If INVPCID is available, use it to flush global mappings Date: Fri, 29 Jan 2016 15:26:25 +0100 Message-ID: <20160129142625.GH10187@pd.tnic> References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Andy Lutomirski Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Brian Gerst , Dave Hansen , Linus Torvalds , Oleg Nesterov , "linux-mm@kvack.org" , Andrey Ryabinin List-Id: linux-mm.kvack.org On Mon, Jan 25, 2016 at 10:37:44AM -0800, Andy Lutomirski wrote: > On my Skylake laptop, INVPCID function 2 (flush absolutely > everything) takes about 376ns, whereas saving flags, twiddling > CR4.PGE to flush global mappings, and restoring flags takes about > 539ns. FWIW, I ran your microbenchmark on the IVB laptop I have here 3 times and some of the numbers from each run are pretty unstable. Not that it means a whole lot - the thing doesn't have INVPCID support. I'm just questioning the microbenchmark and whether we should be rather doing those measurements with a real benchmark, whatever that means. My limited experience says that measuring TLB performance is hard. ./context_switch_latency 0 thread same use_xstate = 0 Using threads 1: 100000 iters at 2676.2 ns/switch 2: 100000 iters at 2700.2 ns/switch 3: 100000 iters at 2656.1 ns/switch ./context_switch_latency 0 thread different use_xstate = 0 Using threads 1: 100000 iters at 5174.8 ns/switch 2: 100000 iters at 5140.5 ns/switch 3: 100000 iters at 5292.9 ns/switch ./context_switch_latency 0 process same use_xstate = 0 Using a subprocess 1: 100000 iters at 2361.2 ns/switch 2: 100000 iters at 2332.2 ns/switch 3: 100000 iters at 3436.9 ns/switch ./context_switch_latency 0 process different use_xstate = 0 Using a subprocess 1: 100000 iters at 4713.6 ns/switch 2: 100000 iters at 4957.5 ns/switch 3: 100000 iters at 5012.2 ns/switch ./context_switch_latency 1 thread same use_xstate = 1 Using threads 1: 100000 iters at 2505.6 ns/switch 2: 100000 iters at 2483.1 ns/switch 3: 100000 iters at 2479.7 ns/switch ./context_switch_latency 1 thread different use_xstate = 1 Using threads 1: 100000 iters at 5245.9 ns/switch 2: 100000 iters at 5241.1 ns/switch 3: 100000 iters at 5220.3 ns/switch ./context_switch_latency 1 process same use_xstate = 1 Using a subprocess 1: 100000 iters at 2329.8 ns/switch 2: 100000 iters at 2350.2 ns/switch 3: 100000 iters at 2500.9 ns/switch ./context_switch_latency 1 process different use_xstate = 1 Using a subprocess 1: 100000 iters at 4970.7 ns/switch 2: 100000 iters at 5034.0 ns/switch 3: 100000 iters at 4991.6 ns/switch -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply.