From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <45BFE2F4.8080309@us.ibm.com> Date: Tue, 30 Jan 2007 18:29:40 -0600 From: Maynard Johnson MIME-Version: 1.0 To: Benjamin Herrenschmidt Subject: Re: [Cbe-oss-dev] [RFC, PATCH 4/4] Add support to OProfile for profiling Cell BE SPUs -- update References: <45BE4ED0.5030808@us.ibm.com> <45BE4FA4.9020105@us.ibm.com> <200701300839.05144.arnd@arndb.de> <45BFBB78.7060907@us.ibm.com> <45BFCC8E.4000008@us.ibm.com> <1170200044.26655.349.camel@localhost.localdomain> In-Reply-To: <1170200044.26655.349.camel@localhost.localdomain> Content-Type: text/plain; charset=us-ascii; format=flowed Cc: linuxppc-dev@ozlabs.org, Arnd Bergmann , cbe-oss-dev@ozlabs.org, oprofile-list@lists.sourceforge.net, linux-kernel@vger.kernel.org Reply-To: maynardj@us.ibm.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Benjamin Herrenschmidt wrote: >>I've given this some more thought, and I'm coming to the conclusion that >>a pure array-based implementation for holding cached_info (getting rid >>of the lists) would work well for the vast majority of cases in which >>OProfile will be used. Yes, it is true that the mapping of an SPU >>context to a phsyical spu-numbered array location cannot be guaranteed >>to stay valid, and that's why I discard the cached_info at that array >>location when the SPU task is switched out. Yes, it would be terribly >>inefficient if the same SPU task gets switched back in later and we >>would have to recreate the cached_info. However, I contend that >>OProfile users are interested in profiling one application at a time. >>They are not going to want to muddy the waters with multiple SPU apps >>running at the same time. I can't think of any reason why someone would >>conscisouly choose to do that. >> >>Any thoughts from the general community, especially OProfile users? > > > Well, it's my understanding that quite a few typical usage scenario > involve different tasks running on different SPUs passing each other > data around. That shouldn't be a problem. I would consider this to be "one large application" consisting of multiple SPU binaries running simultaneously. Such a scenario can be handled with no negative performance impact using a simple 16 element array of cached_info objects -- as long as there isn't (much) SPU task switching being done. -Maynard > > Ben. > >