From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from hr2.samba.org (hr2.samba.org [IPv6:2a01:4f8:192:486::147:1]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3wWRdV64BVzDqLl for ; Mon, 22 May 2017 15:13:34 +1000 (AEST) Date: Mon, 22 May 2017 15:13:13 +1000 From: Anton Blanchard To: Michael Ellerman Cc: benh@kernel.crashing.org, paulus@samba.org, npiggin@gmail.com, mikey@neuling.org, cyrilbur@gmail.com, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH] powerpc/64: Use tick accounting by default Message-ID: <20170522151313.3f60aca2@kryten> In-Reply-To: <87shjxsf0i.fsf@concordia.ellerman.id.au> References: <20170519144112.15649-1-anton@ozlabs.org> <87shjxsf0i.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Hi Michael, > > ppc64 is the only architecture that turns on > > VIRT_CPU_ACCOUNTING_NATIVE by default. The overhead of this option > > is extremely high - a context switch microbenchmark using > > sched_yield() is almost 20% slower. > > Running on what? It should all be nop'ed out unless you're on a > platform that needs it (SPLPAR). POWERNV native. We don't nop out all the vtime_account_* gunk do we? It is all those functions that are a large part of the problem. > > To get finer grained user/hardirq/softirq statitics, the > > IRQ_TIME_ACCOUNTING option can be used instead, which has much lower > > overhead. > > Can it? We don't select HAVE_IRQ_TIME_ACCOUNTING, so AFAICS it can't > be enabled. I have a separate patch to enable it. > Doesn't dropping this mean we never count stolen time? Perhaps. Do we have any applications left that care? Anton