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Peter Anvin" , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt Subject: Re: [PATCH v1 1/1] x86/percpu: Cast -1 to argument type when comparing in percpu_add_op() Message-ID: References: <20240905170356.260300-1-andriy.shevchenko@linux.intel.com> <20241016192011.GY17263@noisy.programming.kicks-ass.net> <20241017181859.GB17263@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241017181859.GB17263@noisy.programming.kicks-ass.net> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo X-Rspam-User: X-Stat-Signature: se6cq5ioumyqautpcj5qracdytr9psci X-Rspamd-Queue-Id: 33AFF14000E X-Rspamd-Server: rspam11 X-HE-Tag: 1729254100-264823 X-HE-Meta: U2FsdGVkX1/E+Vnkr2iZTcS12qCMsGrL/GaGr31yZbz0pX9sGDZtCJbkk2AtkimD+n9wcPbYc+FFFCF3SXEP1qSNNGLw69e4gXbEvsZz/3mDDdjZkSQFCFNIUiQBvJoZBbgrWNOBMnb0ecNB0citKoI8DaUf23Wx9H8hsEv8KuGNp8/ADTT9BT9sjxjNo/1XjddOUASbBBMYKnfsqlaQjzFZzGSAW9jaKljqUqi+cmPJ7KtHAT0g68N90RGhQzmGK0BLhksSjHggj4Bh+puh1SfqgIsvnS2lIaLNWW6FwCm2+COpkDWIaJbkjl9sGW20ouaVezAux3KVjLyBVx217xkw+c+wycKU7KEBcvYrD94vJ2yGbzz7lrDZDaxROXKjjBUeyAQ08j9vsyRFaVXPzw7jCo5GXYmli0VoKNnxybWzAyaNjSpGMOle0OSt8S4L6kEScrKKMxbecqLmCBU09D/J0oFhK5GPRUysIY5/F+uUOUnlnZi3AOkwgytSFE8LwN3UUeEfw/UV6brqpo8N2BwSavWU2KVgXqA4QXD3dXLE45AcNrPpoy3clh8OAnQPeLX4f7l43i6HEBEH8j9IT+A3ZKznn1fVU6GeldIHIbjJWJ54ql5K7YuqJg2QdHvnWPxNuRpnfC5kCSrxeSIFwkOQR1+3R3OKQozvJUo3cN9yOJqiSm5F2fkWP8ncIc8sr671I3k0iyaYfopTLP6ENaatyKxkqySXWW76AFv8LkLypQTfvFVXsQsDkHfXef+Z1PDACGqM4xYh3cQicurogVpkiDoCiZhR+2FeKdshpApX3rC5jRlZP4njIpIjpDoW4uhkAV+M57wL7GuBRnlFVDz8cBAER70Tvcwzf3ep0HSb9Awa3s5TmaSNc+3CGOBawVcg5fBFpRD/9szx9PgFnwkJ0z5IT5oq6DIIW8XajFTLb0BgiabQzSyrCY5DUPy4bdkJjV6UqvAqBtd7TqK 9nmYn8a4 5UuZ6Z0eiVYQXia3MEnr7Nv/NzQD88b7QCZlHHHk0BHPrUd1e0ntXV00sLH5iHyt7rs36DcOeJOzJOdjmnHTVKdFqdyu3OzY4lpItCOQwaqEza89TEXHfxMKgavnv1NeetYIBGdm/Wsq844eGukVfxicVOHd+50tKRmT6GF8HFXnspfGvvjGFpUpNUycwgn5YrA4xrlYiRH4j2enXq/zW21M9XiT5oFaykuqWwTEtxgknAYVHYX0QBjZr5z4foqt+eDlX56vyo2UJHB2xDLEYVn/RVw== 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: List-Subscribe: List-Unsubscribe: On Thu, Oct 17, 2024 at 08:18:59PM +0200, Peter Zijlstra wrote: > On Wed, Oct 16, 2024 at 12:44:18PM -0700, Dave Hansen wrote: > > > Would anybody hate if we broke this up a bit, like: > > > > const typeof(var) _val = val; > > const int paoconst = __builtin_constant_p(val); > > const int paoinc = paoconst && ((_val) == 1); > > const int paodec = paoconst && ((_val) == (typeof(var))-1); > > > > and then did > > > > if (paoinc) > > percpu_unary_op(size, qual, "inc", var); > > ... > > I think that is an overall improvement. Proceed! :-) Wouldn't typeof(var) be a regression? The val can be wider (in term of bits) than var and cutting it like this might bring different result depending on the signedness. TL;DR: Whatever is done, please add more (corner) test cases to the percpu_test.c. -- With Best Regards, Andy Shevchenko