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Mon, 13 Oct 2025 07:50:19 -0400 X-MC-Unique: _Ay75PvOOUKe6IQLG9kgKQ-1 X-Mimecast-MFC-AGG-ID: _Ay75PvOOUKe6IQLG9kgKQ_1760356217 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 367E81956087; Mon, 13 Oct 2025 11:50:17 +0000 (UTC) Received: from fedora (unknown [10.45.226.135]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 0012230002CE; Mon, 13 Oct 2025 11:50:12 +0000 (UTC) Received: by fedora (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 13 Oct 2025 13:50:16 +0200 (CEST) Date: Mon, 13 Oct 2025 13:50:11 +0200 From: Oleg Nesterov To: Peter Zijlstra Cc: Linus Torvalds , Alexander Viro , Boqun Feng , David Howells , Ingo Molnar , Li RongQing , Waiman Long , Will Deacon , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/4] seqlock: introduce scoped_seqlock_read() and scoped_seqlock_read_irqsave() Message-ID: References: <20251009143748.GA2704@redhat.com> <20251009195024.GL3289052@noisy.programming.kicks-ass.net> <20251009201154.GL1386988@noisy.programming.kicks-ass.net> <20251009221242.GX3419281@noisy.programming.kicks-ass.net> <20251010080327.GF4067720@noisy.programming.kicks-ass.net> <20251010122347.GA8798@redhat.com> <20251010131439.GB8798@redhat.com> <20251013090313.GI4067720@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251013090313.GI4067720@noisy.programming.kicks-ass.net> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On 10/13, Peter Zijlstra wrote: > > On Fri, Oct 10, 2025 at 03:14:39PM +0200, Oleg Nesterov wrote: > > static inline void __scoped_seqlock_cleanup(struct ss_tmp *sst) > > { > > if (sst->state & ss_lock) > > spin_unlock(&sst->lock.lock); > > if (sst->state & ss_lock_irqsave) > > spin_unlock_irqrestore(&sst->lock.lock, sst->data); > > } > > > > static inline void > > __scoped_seqlock_next(struct ss_tmp *sst, enum ss_state target) > > { > > switch (sst->state) { > > case ss_lock: > > case ss_lock_irqsave: > > sst->state |= ss_done; > > So GCC is clever enough to see through this scheme, but Clang gets > confused and generates worse code. Specifically it emits the whole > __scoped_seqlock_cleanup() sequence, testing both bits and both unlock > options. OK, thanks and sorry for the noise then. > So while that additional pointer might seem wasteful, it actually makes > the state tracking easier and allows the compiler to more easily throw > away stuff. Great ;) Oleg.