From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 229CC1FB4F for ; Tue, 1 Aug 2023 09:49:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 95730C433CB; Tue, 1 Aug 2023 09:49:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1690883358; bh=yk1dnTiTN5hhO1OfOdeMulKRxehiVlE+uLyY8efFnfo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iYBeseyu8wAu2pNsAOCy1+eCXK/+yEBNrRph2BnWsB6PHk6hRNw3k+aL/UbX7t6V8 wJfZOptFL4bOAqeBkmtGVS6SpSNLJExSYgzzS5ahNE9WWq8yGrW0BNiFe189RC8j4X ix9DU07qRkylahZ1SHw5EI2RNZqkrBgngSLsAD/0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Oleksandr Natalenko , Phil Elwell , Andres Freund , Jens Axboe Subject: [PATCH 6.4 207/239] io_uring: gate iowait schedule on having pending requests Date: Tue, 1 Aug 2023 11:21:11 +0200 Message-ID: <20230801091933.281555192@linuxfoundation.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230801091925.659598007@linuxfoundation.org> References: <20230801091925.659598007@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Jens Axboe commit 7b72d661f1f2f950ab8c12de7e2bc48bdac8ed69 upstream. A previous commit made all cqring waits marked as iowait, as a way to improve performance for short schedules with pending IO. However, for use cases that have a special reaper thread that does nothing but wait on events on the ring, this causes a cosmetic issue where we know have one core marked as being "busy" with 100% iowait. While this isn't a grave issue, it is confusing to users. Rather than always mark us as being in iowait, gate setting of current->in_iowait to 1 by whether or not the waiting task has pending requests. Cc: stable@vger.kernel.org Link: https://lore.kernel.org/io-uring/CAMEGJJ2RxopfNQ7GNLhr7X9=bHXKo+G5OOe0LUq=+UgLXsv1Xg@mail.gmail.com/ Link: https://bugzilla.kernel.org/show_bug.cgi?id=217699 Link: https://bugzilla.kernel.org/show_bug.cgi?id=217700 Reported-by: Oleksandr Natalenko Reported-by: Phil Elwell Tested-by: Andres Freund Fixes: 8a796565cec3 ("io_uring: Use io_schedule* in cqring wait") Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- io_uring/io_uring.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -2579,11 +2579,20 @@ int io_run_task_work_sig(struct io_ring_ return 0; } +static bool current_pending_io(void) +{ + struct io_uring_task *tctx = current->io_uring; + + if (!tctx) + return false; + return percpu_counter_read_positive(&tctx->inflight); +} + /* when returns >0, the caller should retry */ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx, struct io_wait_queue *iowq) { - int token, ret; + int io_wait, ret; if (unlikely(READ_ONCE(ctx->check_cq))) return 1; @@ -2597,17 +2606,19 @@ static inline int io_cqring_wait_schedul return 0; /* - * Use io_schedule_prepare/finish, so cpufreq can take into account - * that the task is waiting for IO - turns out to be important for low - * QD IO. + * Mark us as being in io_wait if we have pending requests, so cpufreq + * can take into account that the task is waiting for IO - turns out + * to be important for low QD IO. */ - token = io_schedule_prepare(); + io_wait = current->in_iowait; + if (current_pending_io()) + current->in_iowait = 1; ret = 0; if (iowq->timeout == KTIME_MAX) schedule(); else if (!schedule_hrtimeout(&iowq->timeout, HRTIMER_MODE_ABS)) ret = -ETIME; - io_schedule_finish(token); + current->in_iowait = io_wait; return ret; }