From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 0BF92211F99B5 for ; Mon, 22 Apr 2019 21:07:06 -0700 (PDT) Date: Tue, 23 Apr 2019 00:07:03 -0400 (EDT) From: Pankaj Gupta Message-ID: <1744824090.22901808.1555992423081.JavaMail.zimbra@redhat.com> In-Reply-To: References: <20190410040826.24371-1-pagupta@redhat.com> <20190418161833.GA22970@infradead.org> Subject: Re: [PATCH v5 1/6] libnvdimm: nd_region flush callback support MIME-Version: 1.0 List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" To: Jeff Moyer Cc: cohuck@redhat.com, Jan Kara , KVM list , "Michael S. Tsirkin" , Jason Wang , david , Qemu Developers , virtualization@lists.linux-foundation.org, Andreas Dilger , Ross Zwisler , Andrea Arcangeli , linux-nvdimm , David Hildenbrand , Matthew Wilcox , Christoph Hellwig , Linux ACPI , linux-ext4 , Len Brown , kilobyte@angband.pl, Rik van Riel , yuval shaia , Stefan Hajnoczi , Paolo Bonzini , lcapitulino@redhat.com, Kevin Wolf , Nitesh Narayan Lal , Theodore Ts'o , Xiao Guangrong , "Darrick J. Wong" , "Rafael J. Wysocki" , Linux Kernel Mailing List , linux-xfs , linux-fsdevel , Igor Mammedov List-ID: > > Dan Williams writes: > > > On Mon, Apr 22, 2019 at 8:59 AM Jeff Moyer wrote: > >> > >> Dan Williams writes: > >> > >> > On Thu, Apr 18, 2019 at 9:18 AM Christoph Hellwig > >> > wrote: > >> >> > >> >> On Thu, Apr 18, 2019 at 09:05:05AM -0700, Dan Williams wrote: > >> >> > > > I'd either add a comment about avoiding retpoline overhead here > >> >> > > > or just > >> >> > > > make ->flush == NULL mean generic_nvdimm_flush(). Just so that > >> >> > > > people don't > >> >> > > > get confused by the code. > >> >> > > > >> >> > > Isn't this premature optimization? I really don't like adding > >> >> > > things > >> >> > > like this without some numbers to show it's worth it. > >> >> > > >> >> > I don't think it's premature given this optimization technique is > >> >> > already being deployed elsewhere, see: > >> >> > > >> >> > https://lwn.net/Articles/774347/ > >> >> > >> >> For one this one was backed by numbers, and second after feedback > >> >> from Linux we switched to the NULL pointer check instead. > >> > > >> > Ok I should have noticed the switch to NULL pointer check. However, > >> > the question still stands do we want everyone to run numbers to > >> > justify this optimization, or make it a new common kernel coding > >> > practice to do: > >> > > >> > if (!object->op) > >> > generic_op(object); > >> > else > >> > object->op(object); > >> > > >> > ...in hot paths? > >> > >> I don't think nvdimm_flush is a hot path. Numbers of some > >> representative workload would prove one of us right. > > > > I'd rather say that the if "if (!op) do_generic()" pattern is more > > readable in the general case, saves grepping for who set the op in the > > common case. The fact that it has the potential to be faster is gravy > > at that point. > > If the primary motivation is performance, then I'd expect performance > numbers to back it up. If that isn't the primary motivation, then > choose whichever way you feel is appropriate. Agree. This change enhances the code readability. Will add this change in v6 with other changes. Thank you! Pankaj > > Cheers, > Jeff > _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm