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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 481A2CA0EEA for ; Fri, 30 Aug 2024 07:43:40 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sjwHp-0003tl-Jj; Fri, 30 Aug 2024 03:43:13 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sjwHn-0003sf-9w for qemu-devel@nongnu.org; Fri, 30 Aug 2024 03:43:11 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sjwHl-00055k-7r for qemu-devel@nongnu.org; Fri, 30 Aug 2024 03:43:11 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1725003788; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=mTVOCFReQ6gJIn9Jq1FWbCKGFU1FOvZoDCRk6jMa65A=; b=KtbMC1MiydGpkolIi3iFYirMYHYYfn+JeTCejcJsn0tG18yErQ6p6HFUk4RAxBv5ikMXru 1NKrsQMx+fABI1IVcjTrli9JAkIfnmm3ilCC6YTnQgm5553xKAcMhuwHSaYkWeslk1fDgY Dy8fJ1ix3Rg0fw+k969XSOx4G+na3pE= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-147-51wYV1y6NLKqnBaLhKP9oQ-1; Fri, 30 Aug 2024 03:43:03 -0400 X-MC-Unique: 51wYV1y6NLKqnBaLhKP9oQ-1 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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 mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A38501955D42; Fri, 30 Aug 2024 07:43:01 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.49]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B6DD91956048; Fri, 30 Aug 2024 07:42:58 +0000 (UTC) Date: Fri, 30 Aug 2024 08:42:55 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Thomas Huth Cc: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Alex =?utf-8?Q?Benn=C3=A9e?= , qemu-devel@nongnu.org, Ani Sinha , Richard Henderson , John Snow , qemu-ppc@nongnu.org, Fabiano Rosas Subject: Re: [PATCH v4 15/35] tests/functional: enable pre-emptive caching of assets Message-ID: References: <20240821082748.65853-1-thuth@redhat.com> <20240821082748.65853-16-thuth@redhat.com> <3a435391-f485-4223-93aa-b937a141db16@linaro.org> <2e2c6480-8a43-4606-b500-2e60bf583d00@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Fri, Aug 30, 2024 at 09:38:17AM +0200, Thomas Huth wrote: > On 29/08/2024 12.15, Daniel P. Berrangé wrote: > > On Tue, Aug 27, 2024 at 04:24:59PM +0200, Thomas Huth wrote: > > > On 27/08/2024 15.16, Thomas Huth wrote: > > > > On 23/08/2024 09.28, Philippe Mathieu-Daudé wrote: > > > > > Hi, > > > > > > > > > > On 21/8/24 10:27, Thomas Huth wrote: > > > > > > From: Daniel P. Berrangé > > > > > > > > > > > > Many tests need to access assets stored on remote sites. We don't want > > > > > > to download these during test execution when run by meson, since this > > > > > > risks hitting test timeouts when data transfers are slow. > > > > > > > > > > > > Add support for pre-emptive caching of assets by setting the env var > > > > > > QEMU_TEST_PRECACHE to point to a timestamp file. When this is set, > > > > > > instead of running the test, the assets will be downloaded and saved > > > > > > to the cache, then the timestamp file created. > ... > > > > > > > > > > When using multiple jobs (-jN) I'm observing some hangs, > > > > > apparently multiple threads trying to download the same file. > > > > > The files are eventually downloaded successfully but it takes > > > > > longer. Should we acquire some exclusive lock somewhere? > > > > > > > > I haven't seen that yet ... what did you exactly run? "make > > > > check-functional -jN" ? Or "make check-functional- -jN" ? > > > > > > After applying some of your patches, I think I've run now into this problem, > > > too: It's because test_aarch64_sbsaref.py and test_aarch64_virt.py try to > > > download the same asset in parallel (alpine-standard-3.17.2-aarch64.iso). > > > > > > Daniel, any ideas how to fix this in the Asset code? > > > > So when downloading we open a file with a ".download" suffix, write to > > that, and then rename it to the final filename. > > > > If we have concurrent usage, both will open the same file and try to > > write to it. Assuming both are downloading the same content we would > > probably "get lucky" and have a consistent file at the end, but clearly > > it is bad to rely on luck. > > > > The lame option is to use NamedTemporaryFile for the teporary file. > > This ensures both processes will write to different temp files, and > > the final rename is atomic. This guarantees safety, but still has > > the double download penalty. > > > > The serious option is to use fcntl.lockf(..., fcntl.LOCK_EX) on the > > temp file. If we can't acquire the lock then just immediately close > > the temp file (don't delete it) and assume another thread is going to > > finish its download. > > > > On windows we'll need msvcrt.locking(..., msvcrt.LK_WLCK, ...) > > instead of fcntl. > > While looking for portable solutions, I noticed that newer versions > of Python have a "x" mode for creating files only if they do not > exist yet. So I think something like this could be a solution: > > @@ -71,17 +72,26 @@ def fetch(self): > tmp_cache_file = self.cache_file.with_suffix(".download") > try: > - resp = urllib.request.urlopen(self.url) > + with tmp_cache_file.open("xb") as dst: > + with urllib.request.urlopen(self.url) as resp: > + copyfileobj(resp, dst) > + except FileExistsError: > + # Another thread already seems to download this asset, > + # so wait until it is done > + self.log.debug("%s already exists, waiting for other thread to finish...", > + tmp_cache_file) > + i = 0 > + while i < 600 and os.path.exists(tmp_cache_file): > + sleep(1) > + i += 1 > + if os.path.exists(self.cache_file): > + return str(self.cache_file) > + raise > except Exception as e: > self.log.error("Unable to download %s: %s", self.url, e) > - raise > - > - try: > - with tmp_cache_file.open("wb+") as dst: > - copyfileobj(resp, dst) > - except: > tmp_cache_file.unlink() > raise > + > try: > # Set these just for informational purposes > os.setxattr(str(tmp_cache_file), "user.qemu-asset-url", > > What do you think, does it look reasonable? The main risk with this, as opposed to fcntl locking, is that it is not crash-safe. If a download is interrupted, subsequent cache runs will wait for a process that doesn't exist to finish downloading and then raise an exception, requiring manual user cleanup of the partial download. Perhaps if we see the tmp_cache_file, and it doesn't change in size after N seconds, we could force unlink it, and create a new download, so we gracefully recover ? With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|