From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 49041C19F21 for ; Wed, 27 Jul 2022 02:02:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233977AbiG0CB6 (ORCPT ); Tue, 26 Jul 2022 22:01:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60906 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229588AbiG0CB4 (ORCPT ); Tue, 26 Jul 2022 22:01:56 -0400 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id F2F2817AA4; Tue, 26 Jul 2022 19:01:52 -0700 (PDT) Received: from kbox (unknown [76.135.27.191]) by linux.microsoft.com (Postfix) with ESMTPSA id 6716D20FE6C1; Tue, 26 Jul 2022 19:01:52 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 6716D20FE6C1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1658887312; bh=bBfPFoDBhzmxwWOcOsa+z7Vs0VyW7iTOA0R6DE9Yyms=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=QFFxRF/PnYQsSn3oCSPsQZmGeL0kCooqNIjdot8w5AJi5JGzdtSyzo3Oan93RRhM7 0UyRz9AZA3/EUmEM6LOFa7vbxRBgcvezp6+BYEqzg1477+FLI+IVbKsMhzHzAvDus8 BHjcoEX9A3CnrOn+jrx04Ou+0i4+//as7gRchHE8= Date: Tue, 26 Jul 2022 19:01:47 -0700 From: Beau Belgrave To: Steven Rostedt Cc: mhiramat@kernel.org, mathieu.desnoyers@efficios.com, linux-trace-devel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org Subject: Re: [PATCH v2 6/7] tracing/user_events: Use bits vs bytes for enabled status page data Message-ID: <20220727020147.GA1705@kbox> References: <20220425184631.2068-1-beaub@linux.microsoft.com> <20220425184631.2068-7-beaub@linux.microsoft.com> <20220726180115.69320865@gandalf.local.home> <20220727000249.GA2289@kbox> <20220726201412.7fbd3b1f@rorschach.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220726201412.7fbd3b1f@rorschach.local.home> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 26, 2022 at 08:14:12PM -0400, Steven Rostedt wrote: > On Tue, 26 Jul 2022 17:02:49 -0700 > Beau Belgrave wrote: > > > > > /* Limit how long of an event name plus args within the subsystem. */ > > > > #define MAX_EVENT_DESC 512 > > > > #define EVENT_NAME(user_event) ((user_event)->tracepoint.name) > > > > #define MAX_FIELD_ARRAY_SIZE 1024 > > > > > > > > +#define STATUS_BYTE(bit) ((bit) >> 3) > > > > +#define STATUS_MASK(bit) (1 << ((bit) & 7)) > > > > + > > > > +/* Internal bits to keep track of connected probes */ > > > > +#define EVENT_STATUS_FTRACE (1 << 0) > > > > +#define EVENT_STATUS_PERF (1 << 1) > > > > +#define EVENT_STATUS_OTHER (1 << 7) > > > > > > Did you mean to shift STATUS_OTHER by 7? > > > > > > > Yes, it should be the value 128. > > > > > Is EVENT_STATUS_OTHER suppose to be one of the flags within the 3 bits of > > > the 7 in STATUS_MASK? > > > > > > > My thought was that STATUS_OTHER would stay on the highest bit. > > Then when we have other systems they would slot into (1 << 2), etc. > > > > This may not be as important now since the byte is never given back to > > the user and is only used when printing out status via the > > user_events_status file in text form. > > So, it is confusing because of STATUS_MASK() is bits 0,1,2 and we are > only using bits 0 and 1, with a OTHER bit at bit 7. And it would be > good to use the BIT() macro. > Ah, I see the confusion. Sorry. EVENT_STATUS_* are internal bits that aren't used with STATUS_MASK or STATUS_BYTE. It's only used to set and check the user event status byte for checking if anything is attached and outputting which probe is connected within the kernel side. STATUS_BYTE and STATUS_MASK take a bit in a bitmap and figure out which byte in the status mapping should be used and which bit in that byte should be set/reset (mask) when it's enabled/disabled via a probe. Both the user and kernel need to align on this logic. IE: Bits above the lower 3 of the index/bit of the event to enable is the byte and the lower 3 bits (& 7) is the actual bit to set. For example if the user_event with the index 1024 is enabled, we need to figure out which byte and bit represents that event when a probe is attached. I got into detail of this in the documentation for both a byte and long wise checking of these values. Hope that helps explain it. > Is STATUS_OTHER suppose to be part of STATUS_MASK()? > > -- Steve Thanks, -Beau