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Message-ID: <x494l73z7th.fsf@segfault.boston.devel.redhat.com> Date: Fri, 12 Apr 2019 09:12:10 -0400 From: Jeff Moyer <jmoyer@...hat.com> To: Jan Kara <jack@...e.cz> Cc: Dan Williams <dan.j.williams@...el.com>, Pankaj Gupta <pagupta@...hat.com>, linux-nvdimm <linux-nvdimm@...ts.01.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, virtualization@...ts.linux-foundation.org, KVM list <kvm@...r.kernel.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, Linux ACPI <linux-acpi@...r.kernel.org>, Qemu Developers <qemu-devel@...gnu.org>, linux-ext4 <linux-ext4@...r.kernel.org>, linux-xfs <linux-xfs@...r.kernel.org>, Ross Zwisler <zwisler@...nel.org>, Vishal L Verma <vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>, "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, Matthew Wilcox <willy@...radead.org>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Christoph Hellwig <hch@...radead.org>, Len Brown <lenb@...nel.org>, Theodore Ts'o <tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca>, "Darrick J. Wong" <darrick.wong@...cle.com>, lcapitulino@...hat.com, Kevin Wolf <kwolf@...hat.com>, Igor Mammedov <imammedo@...hat.com>, Nitesh Narayan Lal <nilal@...hat.com>, Rik van Riel <riel@...riel.com>, Stefan Hajnoczi <stefanha@...hat.com>, Andrea Arcangeli <aarcange@...hat.com>, David Hildenbrand <david@...hat.com>, david <david@...morbit.com>, cohuck@...hat.com, Xiao Guangrong <xiaoguangrong.eric@...il.com>, Paolo Bonzini <pbonzini@...hat.com>, kilobyte@...band.pl, yuval.shaia@...cle.com Subject: Re: [PATCH v5 1/6] libnvdimm: nd_region flush callback support Jan Kara <jack@...e.cz> writes: > On Thu 11-04-19 07:51:48, Dan Williams wrote: >> On Tue, Apr 9, 2019 at 9:09 PM Pankaj Gupta <pagupta@...hat.com> wrote: >> > + } else { >> > + if (nd_region->flush(nd_region)) >> > + rc = -EIO; >> >> Given the common case wants to be fast and synchronous I think we >> should try to avoid retpoline overhead by default. So something like >> this: >> >> if (nd_region->flush == generic_nvdimm_flush) >> rc = generic_nvdimm_flush(...); > > 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. -Jeff
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