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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1E301E748ED for ; Sun, 1 Oct 2023 10:41:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234863AbjJAKlR (ORCPT ); Sun, 1 Oct 2023 06:41:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41588 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234839AbjJAKlL (ORCPT ); Sun, 1 Oct 2023 06:41:11 -0400 Received: from mail-ej1-x636.google.com (mail-ej1-x636.google.com [IPv6:2a00:1450:4864:20::636]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CACBAD9 for ; Sun, 1 Oct 2023 03:41:07 -0700 (PDT) Received: by mail-ej1-x636.google.com with SMTP id a640c23a62f3a-99c136ee106so2134341066b.1 for ; Sun, 01 Oct 2023 03:41:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1696156866; x=1696761666; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=Av1YVGUYjKuKpOxhCUYf9bVAmtK6lNc0JKDBqDmChEQ=; b=XgET2xRhAYWKjiJpGOWCLfXgpro6aiNoftb7Sg8CWyYi8CTIN9sccGA4demrNTykI4 1WuDHXHevQhMSgqzM8j6K1wSZ7q4F1yewjz4LSx4s9KxIxDdZNss3bhS6hltLAeAMTLE g4LO09wTF79iItsrspKUzeGQQM+xU+kRxT2eKmFzmROpB4c17ym3xTK0Nhz6u0ssc0st Av4navrf/a8wcIcFK0vTj1hX3iszFKLkr3banX53nNJYhuh05GqY12FZIyEtrI2BgVFY FbvKN6Qw9oyJ8qYj58qON+5yutp86GR6emR/fs+ZwQ7uoz2whFy6T2S/+V9sqBJUNPle pslg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1696156866; x=1696761666; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=Av1YVGUYjKuKpOxhCUYf9bVAmtK6lNc0JKDBqDmChEQ=; b=Vf0F2lEjY8BwAp+Endmu9Pu9h45AMmC9EUYZ8+7AyaS/XayM01/xpuJLl88vBX7Fnk Gf7cMcJT32oQ8WbyFVf8Ap1G3zNgL9dEyyr+SxB6M1ixhGVI5HqhBosIzV/k81MVM5N+ e33XqaO4Q49xH4QhlkpZp9+gB3Kp+ah/qYfeyeLP0jf4UItNoIVfkw9CzO2ZoHGzmjDy 2+b2J69tny7LIo5W1i8antT+LC/h6flQj7w2UVSa4B8EUkAjXu03OUdKGqbejggLMRSc NgFUJQ5Yb0gf54W2KTtqGCZDycJcJLWj74Nz8gNq+OVhiCMx+mR5Ve+jAPpEKEO4BW62 zbTw== X-Gm-Message-State: AOJu0YzeWDKiIybAwhpX5sne74wN4PgC3Rc+ybw1kFRhepXb4mUOxwu6 Wy3c9Ek/yKBP+7gjuySKQa9JrJQg9dX1fg== X-Google-Smtp-Source: AGHT+IEaRBVRFHBq8PsqtS7Xotm/O/WCU7PUdbnpb1YCwTqlB9U799c5jGmIPkQv2u5NF0F2mavHLA== X-Received: by 2002:a17:906:7695:b0:9ad:e17c:464e with SMTP id o21-20020a170906769500b009ade17c464emr8738266ejm.68.1696156865773; Sun, 01 Oct 2023 03:41:05 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id jx14-20020a170906ca4e00b0099caf5bed64sm15333657ejb.57.2023.10.01.03.41.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 01 Oct 2023 03:41:05 -0700 (PDT) From: Uros Bizjak To: linux-kernel@vger.kernel.org, x86@kernel.org, xen-devel@lists.xenproject.org Cc: Uros Bizjak , Peter Zijlstra , Ingo Molnar , Stefano Stabellini , Oleksandr Tyshchenko , Juergen Gross Subject: [PATCH v2 3/3] xen: Use sync_try_cmpxchg instead of sync_cmpxchg Date: Sun, 1 Oct 2023 12:39:11 +0200 Message-ID: <20231001104053.9644-3-ubizjak@gmail.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20231001104053.9644-1-ubizjak@gmail.com> References: <20231001104053.9644-1-ubizjak@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Use sync_try_cmpxchg instead of sync_cmpxchg (*ptr, old, new) == old in clear_masked_cond(), clear_linked() and gnttab_end_foreign_access_ref_v1(). x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg), improving the cmpxchg loop in gnttab_end_foreign_access_ref_v1 from: 174: eb 0e jmp 184 <...> 176: 89 d0 mov %edx,%eax 178: f0 66 0f b1 31 lock cmpxchg %si,(%rcx) 17d: 66 39 c2 cmp %ax,%dx 180: 74 11 je 193 <...> 182: 89 c2 mov %eax,%edx 184: 89 d6 mov %edx,%esi 186: 66 83 e6 18 and $0x18,%si 18a: 74 ea je 176 <...> to: 614: 89 c1 mov %eax,%ecx 616: 66 83 e1 18 and $0x18,%cx 61a: 75 11 jne 62d <...> 61c: f0 66 0f b1 0a lock cmpxchg %cx,(%rdx) 621: 75 f1 jne 614 <...> No functional change intended. Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Stefano Stabellini Cc: Oleksandr Tyshchenko Acked-by: Juergen Gross Signed-off-by: Uros Bizjak --- v2: Improve commit description. --- drivers/xen/events/events_fifo.c | 26 ++++++++++++-------------- drivers/xen/grant-table.c | 10 ++++------ 2 files changed, 16 insertions(+), 20 deletions(-) diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c index ad9fe51d3fb3..655775db7caf 100644 --- a/drivers/xen/events/events_fifo.c +++ b/drivers/xen/events/events_fifo.c @@ -226,21 +226,20 @@ static bool evtchn_fifo_is_masked(evtchn_port_t port) */ static bool clear_masked_cond(volatile event_word_t *word) { - event_word_t new, old, w; + event_word_t new, old; - w = *word; + old = *word; do { - if (!(w & (1 << EVTCHN_FIFO_MASKED))) + if (!(old & (1 << EVTCHN_FIFO_MASKED))) return true; - if (w & (1 << EVTCHN_FIFO_PENDING)) + if (old & (1 << EVTCHN_FIFO_PENDING)) return false; - old = w & ~(1 << EVTCHN_FIFO_BUSY); + old = old & ~(1 << EVTCHN_FIFO_BUSY); new = old & ~(1 << EVTCHN_FIFO_MASKED); - w = sync_cmpxchg(word, old, new); - } while (w != old); + } while (!sync_try_cmpxchg(word, &old, new)); return true; } @@ -259,17 +258,16 @@ static void evtchn_fifo_unmask(evtchn_port_t port) static uint32_t clear_linked(volatile event_word_t *word) { - event_word_t new, old, w; + event_word_t new, old; - w = *word; + old = *word; do { - old = w; - new = (w & ~((1 << EVTCHN_FIFO_LINKED) - | EVTCHN_FIFO_LINK_MASK)); - } while ((w = sync_cmpxchg(word, old, new)) != old); + new = (old & ~((1 << EVTCHN_FIFO_LINKED) + | EVTCHN_FIFO_LINK_MASK)); + } while (!sync_try_cmpxchg(word, &old, new)); - return w & EVTCHN_FIFO_LINK_MASK; + return old & EVTCHN_FIFO_LINK_MASK; } static void consume_one_event(unsigned cpu, struct evtchn_loop_ctrl *ctrl, diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c index 35659bf70746..04a6b470b15d 100644 --- a/drivers/xen/grant-table.c +++ b/drivers/xen/grant-table.c @@ -427,16 +427,14 @@ EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access); static int gnttab_end_foreign_access_ref_v1(grant_ref_t ref) { - u16 flags, nflags; - u16 *pflags; + u16 *pflags = &gnttab_shared.v1[ref].flags; + u16 flags; - pflags = &gnttab_shared.v1[ref].flags; - nflags = *pflags; + flags = *pflags; do { - flags = nflags; if (flags & (GTF_reading|GTF_writing)) return 0; - } while ((nflags = sync_cmpxchg(pflags, flags, 0)) != flags); + } while (!sync_try_cmpxchg(pflags, &flags, 0)); return 1; } -- 2.41.0