Date:   Wed, 1 Dec 2021 14:50:50 -0500
From:   Bruce Fields <bfields@fieldses.org>
To:     dai.ngo@oracle.com
Cc:     Chuck Lever III <chuck.lever@oracle.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH RFC v5 0/2] nfsd: Initial implementation of NFSv4
 Courteous Server
Message-ID: <20211201195050.GE26415@fieldses.org>
References: <e1093e42-2871-8810-de76-58d1ea357898@oracle.com>
 <C9C6AEC1-641C-4614-B149-5275EFF81C3D@oracle.com>
 <22000fe0-9b17-3d88-1730-c8704417cb92@oracle.com>
 <B42B0F9C-57E2-4F58-8DBD-277636B92607@oracle.com>
 <6f5a060d-17f6-ee46-6546-1217ac5dfa9c@oracle.com>
 <20211130153211.GB8837@fieldses.org>
 <f6a948a7-32d6-da9a-6808-9f2f77d5f792@oracle.com>
 <20211201143630.GB24991@fieldses.org>
 <20211201174205.GB26415@fieldses.org>
 <20211201180339.GC26415@fieldses.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20211201180339.GC26415@fieldses.org>
User-Agent: Mutt/1.5.21 (2010-09-15)
Precedence: bulk

On Wed, Dec 01, 2021 at 01:03:39PM -0500, Bruce Fields wrote:
> On Wed, Dec 01, 2021 at 12:42:05PM -0500, Bruce Fields wrote:
> > On Wed, Dec 01, 2021 at 09:36:30AM -0500, Bruce Fields wrote:
> > > OK, good to know.  It'd be interesting to dig into where nfsdcltrack is
> > > spending its time, which we could do by replacing it with a wrapper that
> > > runs the real nfsdcltrack under strace.
> > > 
> > > Though maybe it'd be better to do this on a system using nfsdcld, since
> > > that's what we're transitioning to.
> > 
> > Trying that on a test VM here, I see each upcall doing 3 fdatasyncs() of
> > an sqlite-journal file.  On my setup, each of those is taking a few
> > milliseconds.  I wonder if it an do better.
> 
> If I understand the sqlite documentation correctly, I *think* that if we
> use journal_mode WAL with synchronous FULL, we should get the assurances
> nfsd needs with one sync per transaction.

So I *think* that would mean just doing something like (untested, don't have
much idea what I'm doing):

diff --git a/utils/nfsdcld/sqlite.c b/utils/nfsdcld/sqlite.c
index 03016fb95823..b30f2614497b 100644
--- a/utils/nfsdcld/sqlite.c
+++ b/utils/nfsdcld/sqlite.c
@@ -826,6 +826,13 @@ sqlite_prepare_dbh(const char *topdir)
                goto out_close;
        }
 
+       ret = sqlite3_exec(dbh, "PRAGMA journal_mode = WAL;", NULL, NULL, NULL);
+       if (ret)
+               goto out_close;
+       ret = sqlite3_exec(dbh, "PRAGMA synchronous = FULL;", NULL, NULL, NULL);
+       if (ret)
+               goto out_close;
+
        ret = sqlite_query_schema_version();
        switch (ret) {
        case CLD_SQLITE_LATEST_SCHEMA_VERSION:

I also wonder how expensive may be the extra overhead of starting up
nfsdcltrack each time.

--b.