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bh=uJ3bFtBX+xFFyPEDv2OXIlVM2+4Lakum4JeZyJHofeI=; b=zHuPw4ApKlRAWEypkg2Ve2Sy10ibX4+DZ70jnonQBEKLHvmpsHiMnB3qY8Ptn9x8IXhsbp dTwyZRWqSYsKgYCKcXcsSbUEwUAVsztza7s1lZpOoxM6sCbTsteIBQjZlizQJWhfCafwrN pzVTughblLnHUMkupvN78oBWNzgMUMZGyyTXCh7b1PJtcX5fmKh8+hx3JDSW+fAQVjBJSj 9IgK1PeZpjTb8BH/L6dJWcVPXNXaXzyimebKYLdUq9iVAXMiSH/pcHIh1/u0s78CWZezw2 HadSQjFkQvt0w+DeLsLQyxFpBuZhoxrEhbQJ3HTM+xumQBVE+/kMft8bMrh9Dw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1695542153; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=uJ3bFtBX+xFFyPEDv2OXIlVM2+4Lakum4JeZyJHofeI=; b=BTG/KIxfrzyYh56D/+yZfbnO+4ToZq5D5hFTY9eyiGzvurxE+tWRjSOgX7QEuQMYxFgZAq W7nsrZV/qTBVZQBA== To: Matthew Wilcox Cc: Linus Torvalds , Peter Zijlstra , Ankur Arora , linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, mgorman@suse.de, rostedt@goodmis.org, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, jgross@suse.com, andrew.cooper3@citrix.com Subject: Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED In-Reply-To: References: <87zg1u1h5t.fsf@oracle.com> <20230911150410.GC9098@noisy.programming.kicks-ass.net> <87h6o01w1a.fsf@oracle.com> <20230912082606.GB35261@noisy.programming.kicks-ass.net> <87cyyfxd4k.ffs@tglx> <87led2wdj0.ffs@tglx> <87h6nkh5bw.ffs@tglx> Date: Sun, 24 Sep 2023 09:55:52 +0200 Message-ID: <878r8wgg3b.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain X-Rspam-User: X-Stat-Signature: q6q1aa4fmtbqaxurq3ypknqrpq5i5neb X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 0092740004 X-HE-Tag: 1695542155-212447 X-HE-Meta: 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 sKgW10/W SobQ8TuaT8cQU3bFPv8HJ0sjsJn0/IZccrPPe6t1WncR9UpUIEZt8sKgMVjNMhskLFW2oAg2/CbJjjGKV5YMS+DDD1LZWFeQ2VbwA X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Sep 24 2023 at 08:19, Matthew Wilcox wrote: > On Sun, Sep 24, 2023 at 12:50:43AM +0200, Thomas Gleixner wrote: >> cond_resched() cannot nest and is obviously scope-less. >> >> The TIF_ALLOW_RESCHED mechanism, which sparked this discussion only >> pretends to be scoped. >> >> As Peter pointed out it does not properly nest with other mechanisms and >> it cannot even nest in itself because it is boolean. > > We can nest a single bit without turning it into a counter -- we > do this for memalloc_nofs_save() for example. Simply return the > current value of the bit, and pass it to _restore(). Right. That works, but the reverse logic still does not make sense: allow_resched(); .... spin_lock(); while resched_now_is_suboptimal(); ... spin_lock(); works. Thanks, tglx