From patchwork Fri Apr 3 01:01:20 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Dixit, Ashutosh" X-Patchwork-Id: 11471725 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 74BE292C for ; Fri, 3 Apr 2020 01:01:25 +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 546B720675 for ; Fri, 3 Apr 2020 01:01:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 546B720675 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 D05806E03F; Fri, 3 Apr 2020 01:01:23 +0000 (UTC) X-Original-To: intel-gfx@lists.freedesktop.org Delivered-To: intel-gfx@lists.freedesktop.org Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by gabe.freedesktop.org (Postfix) with ESMTPS id 2C2C16E03F for ; Fri, 3 Apr 2020 01:01:22 +0000 (UTC) IronPort-SDR: 0yFUhh9Tm7Rc+bF/5MkqDJ30W19qxoicBrpkgJ/hvqlBrxdNI207/VJE17XSRlmY9p7M2uDnNZ 3Dn/y8d5+0iw== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Apr 2020 18:01:21 -0700 IronPort-SDR: HHLqak0NTG76zaWrha5SKbB3nshIratwn5Qn8En9MOLp2dEzOzWXxo1lHBIJ4t7Yy1Rhlzp6R5 tlaVu6HId+Qw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,337,1580803200"; d="scan'208";a="250012602" Received: from adixit-mobl.amr.corp.intel.com (HELO localhost.localdomain) ([10.212.234.39]) by orsmga003.jf.intel.com with ESMTP; 02 Apr 2020 18:01:21 -0700 From: Ashutosh Dixit To: intel-gfx@lists.freedesktop.org Date: Thu, 2 Apr 2020 18:01:20 -0700 Message-Id: <20200403010120.3067-1-ashutosh.dixit@intel.com> X-Mailer: git-send-email 2.25.2 MIME-Version: 1.0 Subject: [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: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" 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) v3: Mistake during patch send (Ashutosh) v4: Remove -EAGAIN from comment (Umesh) v5: Improve condition for clearing pollin and return (Lionel) v6: Improve blocking read loop and other cleanups (Lionel) v7: Added Cc stable Cc: Umesh Nerlige Ramappa Cc: Reviewed-by: Lionel Landwerlin Signed-off-by: Ashutosh Dixit --- drivers/gpu/drm/i915/i915_perf.c | 61 ++++++-------------------------- 1 file changed, 11 insertions(+), 50 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c index 28e3d76fa2e6..2f78b147bb2d 100644 --- a/drivers/gpu/drm/i915/i915_perf.c +++ b/drivers/gpu/drm/i915/i915_perf.c @@ -2963,49 +2963,6 @@ 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 @@ -3031,7 +2988,8 @@ static ssize_t i915_perf_read(struct file *file, { struct i915_perf_stream *stream = file->private_data; struct i915_perf *perf = stream->perf; - ssize_t ret; + size_t offset = 0; + int ret; /* To ensure it's handled consistently we simply treat all reads of a * disabled stream as an error. In particular it might otherwise lead @@ -3054,13 +3012,12 @@ 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); mutex_unlock(&perf->lock); - } while (ret == -EAGAIN); + } while (!offset && !ret); } else { mutex_lock(&perf->lock); - ret = i915_perf_read_locked(stream, file, buf, count, ppos); + ret = stream->ops->read(stream, buf, count, &offset); mutex_unlock(&perf->lock); } @@ -3071,11 +3028,15 @@ 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) + if (ret != -ENOSPC) stream->pollin = false; - return ret; + /* Possible values for ret are 0, -EFAULT, -ENOSPC, -EIO, ... */ + return offset ?: (ret ?: -EAGAIN); } static enum hrtimer_restart oa_poll_check_timer_cb(struct hrtimer *hrtimer)