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Wed, 4 Sep 2019 15:18:43 +0000 From: Huaisheng HS1 Ye To: Mikulas Patocka , "snitzer@redhat.com" CC: "agk@redhat.com" , "prarit@redhat.com" , Tzu ting Yu1 , "dm-devel@redhat.com" , "linux-kernel@vger.kernel.org" , Huaisheng Ye Subject: RE: [External] Re: [PATCH] dm writecache: skip writecache_wait for pmem mode Thread-Topic: [External] Re: [PATCH] dm writecache: skip writecache_wait for pmem mode Thread-Index: AQHVYv2oc/+jfoUYskeMVJQ6yGY6a6cbnUDQ Date: Wed, 4 Sep 2019 15:18:42 +0000 Message-ID: References: <20190902100450.10600-1-yehs2007@zoho.com> In-Reply-To: Accept-Language: zh-CN, en-US Content-Language: zh-CN X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [123.116.211.237] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 6dd07813-6b06-419f-0d0f-08d7314b2c4a x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600166)(711020)(4605104)(1401327)(2017052603328)(7193020);SRVR:SL2PR03MB4427; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 6dd07813-6b06-419f-0d0f-08d7314b2c4a X-MS-Exchange-CrossTenant-originalarrivaltime: 04 Sep 2019 15:18:42.9784 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 5c7d0b28-bdf8-410c-aa93-4df372b16203 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: Ez8odjxltUwioQZQfmDD39QwsEZZEwO6soSo0mOmCjXLNNXbkRsGhYYx09ntvlDmPDznkcWGT9ypJai+u+ZlCA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SL2PR03MB4427 X-OriginatorOrg: lenovo.com Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Mikulas Patocka > Sent: Wednesday, September 4, 2019 4:49 PM > On Mon, 2 Sep 2019, Huaisheng Ye wrote: >=20 > > From: Huaisheng Ye > > > > The array bio_in_progress[2] only have chance to be increased and > > decreased with ssd mode. For pmem mode, they are not involved at all. > > So skip writecache_wait_for_ios in writecache_flush for pmem. > > > > Suggested-by: Doris Yu > > Signed-off-by: Huaisheng Ye > > --- > > drivers/md/dm-writecache.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c > > index c481947..d06b8aa 100644 > > --- a/drivers/md/dm-writecache.c > > +++ b/drivers/md/dm-writecache.c > > @@ -726,7 +726,8 @@ static void writecache_flush(struct dm_writecache *= wc) > > } > > writecache_commit_flushed(wc); > > > > - writecache_wait_for_ios(wc, WRITE); > > + if (!WC_MODE_PMEM(wc)) > > + writecache_wait_for_ios(wc, WRITE); > > > > wc->seq_count++; > > pmem_assign(sb(wc)->seq_count, cpu_to_le64(wc->seq_count)); > > -- > > 1.8.3.1 >=20 > I think this is not needed - wait_event in writecache_wait_for_ios exits > immediatelly if the condition is true. >=20 > This code path is not so hot that we would need microoptimizations like t= his to > avoid function calls. Hi Mikulas, Thanks for your reply, I see what you mean, but I can't agree with you. For pmem mode, this code path (writecache_flush) is much more hot than SSD = mode. Because in the code, the AUTOCOMMIT_BLOCKS_PMEM has been defined to 64, whi= ch means if more than 64 blocks have been inserted to cache device, also ca= lled uncommitted, writecache_flush would be called. Otherwise, there is a timer callback function will be called every 1000 mil= liseconds. #define AUTOCOMMIT_BLOCKS_SSD 65536 #define AUTOCOMMIT_BLOCKS_PMEM 64 #define AUTOCOMMIT_MSEC 1000 So when dm-writecache running in working mode, there are continuous WRITE o= perations has been mapped to writecache_map, writecache_flush will be used = much more often than SSD mode. Cheers, Huaisheng Ye