From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail30t.wh2.ocn.ne.jp ([125.206.180.136]:11261 "HELO mail30t.wh2.ocn.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1761989Ab0GUBCh (ORCPT ); Tue, 20 Jul 2010 21:02:37 -0400 Received: from vs3017.wh2.ocn.ne.jp (125.206.180.250) by mail30t.wh2.ocn.ne.jp (RS ver 1.0.95vs) with SMTP id 4-0157684154 for ; Wed, 21 Jul 2010 10:02:36 +0900 (JST) From: Bruno Randolf To: Bob Copeland Subject: Re: [PATCH/RFC 3/3] ath5k: trace resets Date: Wed, 21 Jul 2010 10:04:59 +0900 Cc: linux-wireless@vger.kernel.org, ath5k-devel@lists.ath5k.org, johannes@sipsolutions.net References: <1279395336-856-1-git-send-email-me@bobcopeland.com> <201007201420.49305.br1@einfach.org> <20100720145200.GB7049@hash.localnet> In-Reply-To: <20100720145200.GB7049@hash.localnet> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Message-Id: <201007211004.59372.br1@einfach.org> Sender: linux-wireless-owner@vger.kernel.org List-ID: On Tue July 20 2010 23:52:00 Bob Copeland wrote: > > again, here my same concerns: printing the reasons for resets is > > something which is useful on embedded boards and production setups which > > can't have tracing enabled. which is why i want to object against this > > change! > > What Johannes said wrt performance: during tracing, only the binary > representations of the data are written to the trace ring buffer, so > unlike the current debug code, we aren't doing printk formatting until > the trace buffer is read. You can save the raw binary data from the > trace and do formatting on another machine. that's true, but try to run a kernel with tracing compiled in and NOT runtime enabled on a small embedded board (soekris net48xx for example) and you'll see the difference. without tracing you can get 22Mbps, with tracing max 15Mbps UDP thruput. that means you cannot run a kernel with tracing enabled on a production system, which also means you cannot log the reasons for a reset there any more. and most of the problems we what to trace (e.g. stuck queue) happen only after days or weeks of operation in production environments... > Another advantage is better granularity: if you only care about watching > tx on the cab queue, you can dynamically filter based on the tracepoint > arguments, something like: > > # echo "qnum == 6" > /debug/tracing/events/ath5k/ath5k_tx/filter > > With the debug printks, you have to hack the driver or grep and hope > the printk buffer didn't overflow and spill what you were looking for. no doubt, i can see the advantages... so let's go ahead with tracing, since we can always build less performant tracing kernels when we want to track down problems. bruno