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 3w7KBb4Pq9zDq5W for ; Wed, 19 Apr 2017 21:13:59 +1000 (AEST) Date: Wed, 19 Apr 2017 21:13:46 +1000 From: Anton Blanchard To: Balbir Singh Cc: Christophe LEROY , mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH] powerpc/configs: Enable function trace by default Message-ID: <20170419211346.5e228370@kryten> In-Reply-To: <1492071568.8380.20.camel@gmail.com> References: <20170413070309.10497-1-bsingharora@gmail.com> <1492071568.8380.20.camel@gmail.com> 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 Balbir, > > FTRACE is quite CPU consumming, shouldn't it really be on by > > default ? > > It does some work at boot to NOP out function entry points at _mcount > locations. Is that what you are referring to? Or the overhead of the > code in terms of size? Most distro kernels have tracing on by default. > > The rest of the overhead is enablement based. Unfortunately the overhead is somewhat high without CONFIG_MPROFILE_KERNEL, and enabling that option will break old toolchains. It would be great if we could automatically enable it based on the toolchain. Even with CONFIG_MPROFILE_KERNEL enabled, we aren't noping out the redundant mflr at the start of each function. Anton