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 X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3BF8FC43331 for ; Thu, 26 Mar 2020 09:09:40 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 183262070A for ; Thu, 26 Mar 2020 09:09:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 183262070A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=intel-gfx-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id CB2686E894; Thu, 26 Mar 2020 09:09:38 +0000 (UTC) Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by gabe.freedesktop.org (Postfix) with ESMTPS id AC15F6E894 for ; Thu, 26 Mar 2020 09:09:37 +0000 (UTC) IronPort-SDR: /jOuNRR2jBt06SSpDcO5y2h1oglAReXNNORGqDyTkXUom4oraHtSl6LhfjqXoqO2M9u9N223Ai +a02dLBk15pw== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Mar 2020 02:09:36 -0700 IronPort-SDR: lZroT+RMKu4hWosViyqUKryFrTXtw4fJzXCBp2VU6LiKKtqh5sok41kGOG358Uxb59vdJY4Coa iy+h67JdD+ww== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,307,1580803200"; d="scan'208";a="282433881" Received: from aschoene-mobl.ger.corp.intel.com (HELO [10.252.56.206]) ([10.252.56.206]) by fmsmga002.fm.intel.com with ESMTP; 26 Mar 2020 02:09:35 -0700 To: Ashutosh Dixit , intel-gfx@lists.freedesktop.org References: <6ec4772094094bb6967f0bd68e68c5e9e5613557.1585197556.git.ashutosh.dixit@intel.com> From: Lionel Landwerlin Organization: Intel Corporation (UK) Ltd. - Co. Reg. #1134945 - Pipers Way, Swindon SN3 1RJ Message-ID: <60dd3f4f-7728-89eb-d582-19232967a8bb@intel.com> Date: Thu, 26 Mar 2020 11:09:34 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <6ec4772094094bb6967f0bd68e68c5e9e5613557.1585197556.git.ashutosh.dixit@intel.com> Content-Language: en-US Subject: Re: [Intel-gfx] [PATCH] drm/i915/perf: Do not clear pollin for small user read buffers X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 26/03/2020 06:43, Ashutosh Dixit wrote: > It is wrong to block the user thread in the next poll when OA data is > already available which could not fit in the user buffer provided in > the previous read. In several cases the exact user buffer size is not > known. Blocking user space in poll can lead to data loss when the > buffer size used is smaller than the available data. > > This change fixes this issue and allows user space to read all OA data > even when using a buffer size smaller than the available data using > multiple non-blocking reads rather than staying blocked in poll till > the next timer interrupt. > > v2: Fix ret value for blocking reads (Umesh) > > Cc: Umesh Nerlige Ramappa > Cc: Lionel Landwerlin > Signed-off-by: Ashutosh Dixit > --- > drivers/gpu/drm/i915/i915_perf.c | 63 ++++++-------------------------- > 1 file changed, 12 insertions(+), 51 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c > index 3222f6cd8255..e2d083efba6d 100644 > --- a/drivers/gpu/drm/i915/i915_perf.c > +++ b/drivers/gpu/drm/i915/i915_perf.c > @@ -2957,49 +2957,6 @@ void i915_oa_init_reg_state(const struct intel_context *ce, > gen8_update_reg_state_unlocked(ce, stream); > } > > -/** > - * i915_perf_read_locked - &i915_perf_stream_ops->read with error normalisation > - * @stream: An i915 perf stream > - * @file: An i915 perf stream file > - * @buf: destination buffer given by userspace > - * @count: the number of bytes userspace wants to read > - * @ppos: (inout) file seek position (unused) > - * > - * Besides wrapping &i915_perf_stream_ops->read this provides a common place to > - * ensure that if we've successfully copied any data then reporting that takes > - * precedence over any internal error status, so the data isn't lost. > - * > - * For example ret will be -ENOSPC whenever there is more buffered data than > - * can be copied to userspace, but that's only interesting if we weren't able > - * to copy some data because it implies the userspace buffer is too small to > - * receive a single record (and we never split records). > - * > - * Another case with ret == -EFAULT is more of a grey area since it would seem > - * like bad form for userspace to ask us to overrun its buffer, but the user > - * knows best: > - * > - * http://yarchive.net/comp/linux/partial_reads_writes.html > - * > - * Returns: The number of bytes copied or a negative error code on failure. > - */ > -static ssize_t i915_perf_read_locked(struct i915_perf_stream *stream, > - struct file *file, > - char __user *buf, > - size_t count, > - loff_t *ppos) > -{ > - /* Note we keep the offset (aka bytes read) separate from any > - * error status so that the final check for whether we return > - * the bytes read with a higher precedence than any error (see > - * comment below) doesn't need to be handled/duplicated in > - * stream->ops->read() implementations. > - */ > - size_t offset = 0; > - int ret = stream->ops->read(stream, buf, count, &offset); > - > - return offset ?: (ret ?: -EAGAIN); > -} > - > /** > * i915_perf_read - handles read() FOP for i915 perf stream FDs > * @file: An i915 perf stream file > @@ -3025,6 +2982,8 @@ static ssize_t i915_perf_read(struct file *file, > { > struct i915_perf_stream *stream = file->private_data; > struct i915_perf *perf = stream->perf; > + size_t offset = 0; > + int __ret; > ssize_t ret; > > /* To ensure it's handled consistently we simply treat all reads of a > @@ -3048,16 +3007,19 @@ static ssize_t i915_perf_read(struct file *file, > return ret; > > mutex_lock(&perf->lock); > - ret = i915_perf_read_locked(stream, file, > - buf, count, ppos); > + __ret = stream->ops->read(stream, buf, count, &offset); > + ret = offset ?: (__ret ?: -EAGAIN); > mutex_unlock(&perf->lock); > } while (ret == -EAGAIN); > } else { > mutex_lock(&perf->lock); > - ret = i915_perf_read_locked(stream, file, buf, count, ppos); > + __ret = stream->ops->read(stream, buf, count, &offset); > + ret = offset ?: (__ret ?: -EAGAIN); > mutex_unlock(&perf->lock); > } > > + /* Possible values for __ret are 0, -EFAULT, -ENOSPC, -EAGAIN, ... */ > + > /* We allow the poll checking to sometimes report false positive EPOLLIN > * events where we might actually report EAGAIN on read() if there's > * not really any data available. In this situation though we don't > @@ -3065,13 +3027,12 @@ static ssize_t i915_perf_read(struct file *file, > * and read() returning -EAGAIN. Clearing the oa.pollin state here > * effectively ensures we back off until the next hrtimer callback > * before reporting another EPOLLIN event. > + * The exception to this is if ops->read() returned -ENOSPC which means > + * that more OA data is available than could fit in the user provided > + * buffer. In this case we want the next poll() call to not block. > */ > - if (ret >= 0 || ret == -EAGAIN) { > - /* Maybe make ->pollin per-stream state if we support multiple > - * concurrent streams in the future. > - */ > + if ((ret > 0 || ret == -EAGAIN) && __ret != -ENOSPC) > stream->pollin = false; > - } > > return ret; > } I think this reset of the pollin field is in the wrong place in the driver. The decision of whether pollin is true/false should be based off the difference between head/tail pointers. In my opinion the best place to do this in at the end of gen7/8_append_oa_reports functions, under the stream->oa_buffer.ptr_lock. If everything has been read up to the tail pointer, then there is nothing to wake up userspace for, otherwise leave pollin untouched. -Lionel _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx