From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bmailout1.hostsharing.net (bmailout1.hostsharing.net [83.223.95.100]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 61E561D699; Thu, 4 Jan 2024 07:02:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=wunner.de Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=h08.hostsharing.net Received: from h08.hostsharing.net (h08.hostsharing.net [83.223.95.28]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "*.hostsharing.net", Issuer "RapidSSL TLS RSA CA G1" (verified OK)) by bmailout1.hostsharing.net (Postfix) with ESMTPS id 8489130000D0B; Thu, 4 Jan 2024 08:02:35 +0100 (CET) Received: by h08.hostsharing.net (Postfix, from userid 100393) id 67757239FE7; Thu, 4 Jan 2024 08:02:35 +0100 (CET) Date: Thu, 4 Jan 2024 08:02:35 +0100 From: Lukas Wunner To: Dan Williams Cc: Ira Weiny , Jonathan Cameron , Smita Koralahalli , Shiju Jose , Yazen Ghannam , Davidlohr Bueso , Dave Jiang , Alison Schofield , Vishal Verma , Ard Biesheuvel , linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, Bjorn Helgaas Subject: Re: [PATCH v5 8/9] PCI: Define scoped based management functions Message-ID: <20240104070235.GA13468@wunner.de> References: <20231220-cxl-cper-v5-0-1bb8a4ca2c7a@intel.com> <20231220-cxl-cper-v5-8-1bb8a4ca2c7a@intel.com> <20240104060528.GA10504@wunner.de> <6596539c9729e_8dc6829476@dwillia2-xfh.jf.intel.com.notmuch> 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: <6596539c9729e_8dc6829476@dwillia2-xfh.jf.intel.com.notmuch> User-Agent: Mutt/1.10.1 (2018-07-13) On Wed, Jan 03, 2024 at 10:43:40PM -0800, Dan Williams wrote: > Lukas Wunner wrote: > > On Wed, Dec 20, 2023 at 04:17:35PM -0800, Ira Weiny wrote: > > > --- a/include/linux/pci.h > > > +++ b/include/linux/pci.h > > > @@ -1170,6 +1170,7 @@ int pci_get_interrupt_pin(struct pci_dev *dev, struct pci_dev **bridge); > > > u8 pci_common_swizzle(struct pci_dev *dev, u8 *pinp); > > > struct pci_dev *pci_dev_get(struct pci_dev *dev); > > > void pci_dev_put(struct pci_dev *dev); > > > +DEFINE_FREE(pci_dev_put, struct pci_dev *, if (_T) pci_dev_put(_T)) > > > > pci_dev_put() already performs a NULL pointer check internally. > > Why duplicate it here? > > Greg asked the same for the introduction of __free(kvfree), and Peter > clarified: > > http://lore.kernel.org/r/20230814161731.GN776869@hirez.programming.kicks-ass.net > > Essentially, that check is more for build-time than runtime because when > the macro is expanded the compiler can notice scenarios where @pdev is > set to NULL (likely by no_free_ptr()) and skip the call to pci_dev_put() > altogether. pci_dev_put() also happens to be out-of-line, so saving a > call when @pdev is NULL a small win in that respect as well. Doubtful whether that's correct. The kernel is compiled with -fno-delete-null-pointer-checks since commit a3ca86aea507 ("Add '-fno-delete-null-pointer-checks' to gcc CFLAGS"). So these NULL pointer checks are generally not optimized away. I've just responded to the discussion you've linked above: https://lore.kernel.org/all/20240104065744.GA6055@wunner.de/ Thanks, Lukas