Return-Path: linux-nfs-owner@vger.kernel.org Received: from mx142.netapp.com ([216.240.21.19]:3904 "EHLO mx142.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754193AbbBEQxn (ORCPT ); Thu, 5 Feb 2015 11:53:43 -0500 Message-ID: <54D3A015.7040207@Netapp.com> Date: Thu, 5 Feb 2015 11:53:41 -0500 From: Anna Schumaker MIME-Version: 1.0 To: "J. Bruce Fields" CC: Christoph Hellwig , Subject: Re: [PATCH v2 2/4] NFSD: Add READ_PLUS support for data segments References: <1422477777-27933-1-git-send-email-Anna.Schumaker@Netapp.com> <1422477777-27933-3-git-send-email-Anna.Schumaker@Netapp.com> <20150205141325.GC4522@infradead.org> <54D394EC.9030902@Netapp.com> <20150205162326.GA18977@infradead.org> <54D39DC2.9060808@Netapp.com> <20150205164832.GB4289@fieldses.org> In-Reply-To: <20150205164832.GB4289@fieldses.org> Content-Type: text/plain; charset="utf-8" Sender: linux-nfs-owner@vger.kernel.org List-ID: On 02/05/2015 11:48 AM, J. Bruce Fields wrote: > On Thu, Feb 05, 2015 at 11:43:46AM -0500, Anna Schumaker wrote: >> On 02/05/2015 11:23 AM, Christoph Hellwig wrote: >>> On Thu, Feb 05, 2015 at 11:06:04AM -0500, Anna Schumaker wrote: >>>>> If the READ_PLUS implementation can't use the splice read path it's >>>>> probably a loss for most workloads. >>>>> >>>> >>>> I'll play around with the splice path, but I don't think it was designed for encoding multiple read segments. >>> >>> The problem is that the typical case of all data won't use splice >>> every with your patches as the 4.2 client will always send a READ_PLUS. >>> >>> So we'll have to find a way to use it where it helps. While we might be >>> able to add some hacks to only use splice for the first segment I guess >>> we just need to make the splice support generic enough in the long run. >>> >> >> I should be able to use splice if I detect that we're only returning a single DATA segment easily enough. > > Oh, good thought, yes maybe that would be enough. > > But I still wish he had more evidence here. I'm planning to do some performance testing with this change: diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c index e2a4702..f516694 100644 --- a/fs/nfsd/nfs4xdr.c +++ b/fs/nfsd/nfs4xdr.c @@ -3876,7 +3876,10 @@ nfsd4_encode_read_plus_data(struct nfsd4_compoundres *resp, struct nfsd4_read *r maxcount = min_t(unsigned long, maxcount, read->rd_length); maxcount = min_t(unsigned long, maxcount, hole_pos - read->rd_offset); - err = nfsd4_encode_readv(resp, read, file, &maxcount); + if ((read->rd_offset == 0) && (read->rd_length == maxcount)) + err = nfsd4_encode_splice_read(resp, read, file, &maxcount); + else + err = nfsd4_encode_readv(resp, read, file, &maxcount); *p++ = cpu_to_be32(NFS4_CONTENT_DATA); p = xdr_encode_hyper(p, read->rd_offset); > > --b. >