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[2620:137:e000::1:20]) by mx.google.com with ESMTP id sh6-20020a1709076e8600b00870b0d90078si10139179ejc.644.2023.01.18.07.10.15; Wed, 18 Jan 2023 07:10:40 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20210112 header.b=Tn84+dn0; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230236AbjARPHX (ORCPT + 99 others); Wed, 18 Jan 2023 10:07:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39038 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229910AbjARPHT (ORCPT ); Wed, 18 Jan 2023 10:07:19 -0500 Received: from mail-ed1-x52f.google.com (mail-ed1-x52f.google.com [IPv6:2a00:1450:4864:20::52f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E97BB196B2 for ; Wed, 18 Jan 2023 07:07:13 -0800 (PST) Received: by mail-ed1-x52f.google.com with SMTP id v30so50008877edb.9 for ; Wed, 18 Jan 2023 07:07:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=de5VSyCSp4LwIkgkLbu8PgcqKtOJrMJR3VqjQzZBt04=; b=Tn84+dn0XpHVthmT5dogJZCrr7OsRwjBMD8hbBUwdImvjTCgvCNeA+K4edPl83CnGu 2ZTUVsS9miwka1IP8rdQnBaK2FLqudjX2Ht/h205Xg2sLCWXlkRTJZ2Fz05i7SPOc7zu UiT2s99aNP7pm72NtR9ZlPS0oOCzBaEnu+5a27TOOi3H+1rCaY1+3G80NGB2+hMyH0jf KobfxgPJvrH2cvKvJOEqRFAWGtwJOo8YhRqmY76mYm1Er2eRVYPebDkhQZqAu7h3ElgP JROiD+bp4Y9u66ioDV4aKzfLZdKVgWRJhWSLxvC7+Bf5qYhSc7LS1Uak1H9soeJrygE6 R8NQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=de5VSyCSp4LwIkgkLbu8PgcqKtOJrMJR3VqjQzZBt04=; b=TLy5a7/QcpiZ4gM0ypFwT4e7pI0UPd11/r3acriVzx6DF9tFN/oznuhRIJFLpL7Tsy baIFDI6k6cViHTa3VW5SZ7kVXCPl2iRO8Bw+cpw2UGc53MY9DYVWyYNA2kWt3EPbqcYK 5dF8c/VXTvDu1GTOSFTFn+aK6mRF9GaPoniYSsmPMMWMkqwMmvdouDpL2pPVPYc8aJ+2 FcfR4JyL4tn67SP9UWbGnhUdI/2VWbkmAbDsavPmBMnkQueEz6NhzbQI8oO2qyY8YcrI lwVttQKpaxves9ALvfFAmxzAE8VgU76rlENdUHRT0VaFPtNa4NYbSUhg1/eiTSWnXhW0 eZdw== X-Gm-Message-State: AFqh2kouywBluueXVmQVFeHkpZBbt4039EQu4Rj3R3ljW7F3i1R4ko9w gO97qAucqOPt9c0L9H2JREjKlutl8RR6RA== X-Received: by 2002:aa7:c3cf:0:b0:499:5405:9319 with SMTP id l15-20020aa7c3cf000000b0049954059319mr6980786edr.32.1674054432104; Wed, 18 Jan 2023 07:07:12 -0800 (PST) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id m20-20020aa7c2d4000000b00495f4535a33sm14425184edp.74.2023.01.18.07.07.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Jan 2023 07:07:11 -0800 (PST) From: Uros Bizjak To: linux-kernel@vger.kernel.org Cc: Uros Bizjak , Andrew Morton Subject: [PATCH] lib/genalloc: use try_cmpxchg in {set,clear}_bits_ll Date: Wed, 18 Jan 2023 16:07:03 +0100 Message-Id: <20230118150703.4024-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.39.0 MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM, RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1755373518849416807?= X-GMAIL-MSGID: =?utf-8?q?1755373518849416807?= Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in {set,clear}_bits_ll. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails. Note that the value from *ptr should be read using READ_ONCE to prevent the compiler from merging, refetching or reordering the read. The patch also declares these two functions inline, to ensure inlining. No functional change intended. Signed-off-by: Uros Bizjak Cc: Andrew Morton --- lib/genalloc.c | 18 ++++++++---------- 1 file changed, 8 insertions(+), 10 deletions(-) diff --git a/lib/genalloc.c b/lib/genalloc.c index 00fc50d0a640..0c883d6fbd44 100644 --- a/lib/genalloc.c +++ b/lib/genalloc.c @@ -40,32 +40,30 @@ static inline size_t chunk_size(const struct gen_pool_chunk *chunk) return chunk->end_addr - chunk->start_addr + 1; } -static int set_bits_ll(unsigned long *addr, unsigned long mask_to_set) +static inline int +set_bits_ll(unsigned long *addr, unsigned long mask_to_set) { - unsigned long val, nval; + unsigned long val = READ_ONCE(*addr); - nval = *addr; do { - val = nval; if (val & mask_to_set) return -EBUSY; cpu_relax(); - } while ((nval = cmpxchg(addr, val, val | mask_to_set)) != val); + } while (!try_cmpxchg(addr, &val, val | mask_to_set)); return 0; } -static int clear_bits_ll(unsigned long *addr, unsigned long mask_to_clear) +static inline int +clear_bits_ll(unsigned long *addr, unsigned long mask_to_clear) { - unsigned long val, nval; + unsigned long val = READ_ONCE(*addr); - nval = *addr; do { - val = nval; if ((val & mask_to_clear) != mask_to_clear) return -EBUSY; cpu_relax(); - } while ((nval = cmpxchg(addr, val, val & ~mask_to_clear)) != val); + } while (!try_cmpxchg(addr, &val, val & ~mask_to_clear)); return 0; }