From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from simark.ca by simark.ca with LMTP id TN9pB4ZepWC8QQAAWB0awg (envelope-from ) for ; Wed, 19 May 2021 14:52:54 -0400 Received: by simark.ca (Postfix, from userid 112) id 1124C1F11C; Wed, 19 May 2021 14:52:54 -0400 (EDT) X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on simark.ca X-Spam-Level: X-Spam-Status: No, score=-1.1 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.2 Received: from lists.lttng.org (lists.lttng.org [167.114.26.123]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by simark.ca (Postfix) with ESMTPS id 55B631E783 for ; Wed, 19 May 2021 14:52:53 -0400 (EDT) Received: from lists-lttng01.efficios.com (localhost [IPv6:::1]) by lists.lttng.org (Postfix) with ESMTP id 4Flhnw5v1xz1r80; Wed, 19 May 2021 14:52:52 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=lists.lttng.org; s=default; t=1621450373; bh=8bsDeJ0qMMJn74/0pbSHLZd9wTrR5AVZeDdLCgDnWKY=; h=Date:To:Cc:In-Reply-To:References:Subject:List-Id: List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe: From:Reply-To:From; b=EXtn0nrr3Ci8s6RbksivCJ9ViaDKx+e6ZKL4OZsPCGr4q7R2l9BKgEBuj+bWiix0A cwxReXpxBYYS/YHo+a8inTxFNHyrhW9G8SSxC1VFmXJvxtH/NJW/ucyCtjhmGwAmJJ GKSJTlBheZemryugD/+21pHMBTy5Y+4wZIhrMYU6BKKlVfaNLkcIJdd2HSBdBi7aXa n//9ym2KUNlpA2StcPvMATHHV0gwrfgOQEmYD0Dg9VtG+W4jbQFOJJiUs9szAuKxx1 kyHdTk06+ZLbFFLcs5vjJCA6S074L4+hPlzyIFvDwqGAf9t68dshHhFAOQ64c9M1JU p9zOU+Nwr5sSw== Received: from mail.efficios.com (mail.efficios.com [167.114.26.124]) by lists.lttng.org (Postfix) with ESMTPS id 4Flhnw4cG9z1r6L for ; Wed, 19 May 2021 14:52:52 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 2D60F32DFAE for ; Wed, 19 May 2021 14:52:46 -0400 (EDT) Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id EEWkpuRikxxn; Wed, 19 May 2021 14:52:45 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id CA17832E019; Wed, 19 May 2021 14:52:45 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com CA17832E019 X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id W_ojtFefBKrD; Wed, 19 May 2021 14:52:45 -0400 (EDT) Received: from mail03.efficios.com (mail03.efficios.com [167.114.26.124]) by mail.efficios.com (Postfix) with ESMTP id BCA2B32DC28; Wed, 19 May 2021 14:52:45 -0400 (EDT) Date: Wed, 19 May 2021 14:52:45 -0400 (EDT) To: Norbert Lange Cc: lttng-dev Message-ID: <217443874.51651.1621450365666.JavaMail.zimbra@efficios.com> In-Reply-To: References: MIME-Version: 1.0 X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_4018 (ZimbraWebClient - FF88 (Linux)/8.8.15_GA_4007) Thread-Topic: reading context fields causes syscalls Thread-Index: aTyJxyZBRNwWlNLtU8JIdDhX38xJ3A== Subject: Re: [lttng-dev] reading context fields causes syscalls X-BeenThere: lttng-dev@lists.lttng.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: LTTng development list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Mathieu Desnoyers via lttng-dev Reply-To: Mathieu Desnoyers Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" ----- On May 19, 2021, at 8:11 AM, lttng-dev lttng-dev@lists.lttng.org wrote: > Hello, > > Several context fields will cause a syscall atleast the first time a > tracepoint is > recorded. For example all of the following: > > `lttng add-context -c chan --userspace --type=vpid --type=vtid --type=procname` > > Each of them seems cached in TLS however, and most should never change > after startup. > > As I am using Lttng over Xenomai, syscalls are strictly forbidden, I > would like to have some function that prepares all data, which I can > call on each thread before it switches to realtime work. > > Kinda similar to urcu_bp_register_thread, I'd like to have some > `lttng_ust_warmup_thread` function that fetches the context values > that can be cached. (urcu_bp_register_thread should be called there > aswell) > I considered just doing a tracepoint, but AFAIK the channel can be > changed/configured after the process is running. So this is not robust > enough. The new lttng_ust_init_thread() API in lttng-ust 2.13 would be the right place to do this I think: /* * Initialize this thread's LTTng-UST data structures. There is * typically no need to call this, because LTTng-UST initializes its * per-thread data structures lazily, but it should be called explicitly * upon creation of each thread before signal handlers nesting over * those threads use LTTng-UST tracepoints. */ It would make sense that this new initialization helper also initializes all contexts which cache the result of a system call. Considering that contexts can be used from the filter and capture bytecode interpreter, as well as contexts added to channels, I think we'd need to simply initialize them all. Thanks, Mathieu > > regards, Norbert > _______________________________________________ > lttng-dev mailing list > lttng-dev@lists.lttng.org > https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev