From patchwork Fri Jan 20 14:03:47 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kent Overstreet X-Patchwork-Id: 13109899 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7F456C05027 for ; Fri, 20 Jan 2023 14:04:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229883AbjATOEA (ORCPT ); Fri, 20 Jan 2023 09:04:00 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32826 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229590AbjATOD7 (ORCPT ); Fri, 20 Jan 2023 09:03:59 -0500 Received: from out2.migadu.com (out2.migadu.com [IPv6:2001:41d0:2:aacc::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 08F5A10F4; Fri, 20 Jan 2023 06:03:57 -0800 (PST) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1674223435; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=sy7eMQzxcTa/bh+mUhi76yBRMuqFbyrbkkHTHv1Udhg=; b=f7AHZlnjAPNNXFg75Batm8SpXClWMYWFjfBADNg8RH4JTrffz3mU0HurWjRmqY7J7KSi8P sfKfNL7HsEUAgBh6z0PCQabIHjliW3GFo7x6k3M+basy3JzRdyC+kHTAzLrkaK2KmprkgH 3HyWnD3v99v1NZfXDf3iLShugGzZ3lY= From: Kent Overstreet To: linux-kernel@vger.kernel.org Cc: Kent Overstreet , linux-aio@kvack.org, linux-fsdevel@vger.kernel.org Subject: [PATCH v2] fs/aio: obey min_nr when doing wakeups Date: Fri, 20 Jan 2023 09:03:47 -0500 Message-Id: <20230120140347.2133611-1-kent.overstreet@linux.dev> In-Reply-To: <20230118152603.28301-1-kent.overstreet@linux.dev> References: <20230118152603.28301-1-kent.overstreet@linux.dev> MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org I've been observing workloads where IPIs due to wakeups in aio_complete() are ~15% of total CPU time in the profile. Most of those wakeups are unnecessary when completion batching is in use in io_getevents(). This plumbs min_nr through via the wait eventry, so that aio_complete() can avoid doing unnecessary wakeups. v2: This fixes a race in the first version of the patch. If we read some events out after adding to the waitlist, we need to update wait.min_nr call prepare_to_wait_event() again before scheduling. Signed-off-by: Kent Overstreet Cc: Benjamin LaHaise ki_ctx; struct aio_ring *ring; struct io_event *ev_page, *event; - unsigned tail, pos, head; + unsigned tail, pos, head, avail; unsigned long flags; /* @@ -1157,6 +1162,10 @@ static void aio_complete(struct aio_kiocb *iocb) ctx->completed_events++; if (ctx->completed_events > 1) refill_reqs_available(ctx, head, tail); + + avail = tail > head + ? tail - head + : tail + ctx->nr_events - head; spin_unlock_irqrestore(&ctx->completion_lock, flags); pr_debug("added to ring %p at [%u]\n", iocb, tail); @@ -1177,8 +1186,18 @@ static void aio_complete(struct aio_kiocb *iocb) */ smp_mb(); - if (waitqueue_active(&ctx->wait)) - wake_up(&ctx->wait); + if (waitqueue_active(&ctx->wait)) { + struct aio_waiter *curr, *next; + unsigned long flags; + + spin_lock_irqsave(&ctx->wait.lock, flags); + list_for_each_entry_safe(curr, next, &ctx->wait.head, w.entry) + if (avail >= curr->min_nr) { + list_del_init_careful(&curr->w.entry); + wake_up_process(curr->w.private); + } + spin_unlock_irqrestore(&ctx->wait.lock, flags); + } } static inline void iocb_put(struct aio_kiocb *iocb) @@ -1294,7 +1313,9 @@ static long read_events(struct kioctx *ctx, long min_nr, long nr, struct io_event __user *event, ktime_t until) { - long ret = 0; + struct hrtimer_sleeper t; + struct aio_waiter w; + long ret = 0, ret2 = 0; /* * Note that aio_read_events() is being called as the conditional - i.e. @@ -1310,12 +1331,37 @@ static long read_events(struct kioctx *ctx, long min_nr, long nr, * the ringbuffer empty. So in practice we should be ok, but it's * something to be aware of when touching this code. */ - if (until == 0) - aio_read_events(ctx, min_nr, nr, event, &ret); - else - wait_event_interruptible_hrtimeout(ctx->wait, - aio_read_events(ctx, min_nr, nr, event, &ret), - until); + aio_read_events(ctx, min_nr, nr, event, &ret); + if (until == 0 || ret < 0 || ret >= min_nr) + return ret; + + hrtimer_init_sleeper_on_stack(&t, CLOCK_MONOTONIC, HRTIMER_MODE_REL); + if (until != KTIME_MAX) { + hrtimer_set_expires_range_ns(&t.timer, until, current->timer_slack_ns); + hrtimer_sleeper_start_expires(&t, HRTIMER_MODE_REL); + } + + init_wait(&w.w); + + while (1) { + unsigned long nr_got = ret; + + w.min_nr = min_nr - ret; + + ret2 = prepare_to_wait_event(&ctx->wait, &w.w, TASK_INTERRUPTIBLE) ?: + !t.task ? -ETIME : 0; + + if (aio_read_events(ctx, min_nr, nr, event, &ret) || ret2) + break; + + if (nr_got == ret) + schedule(); + } + + finish_wait(&ctx->wait, &w.w); + hrtimer_cancel(&t.timer); + destroy_hrtimer_on_stack(&t.timer); + return ret; }