From mboxrd@z Thu Jan 1 00:00:00 1970 From: Song Liu Subject: Re: [PATCH v2] scsi: ses: don't get power status of SES device slot on probe Date: Wed, 5 Apr 2017 16:23:46 +0000 Message-ID: References: <1491405499-5429-1-git-send-email-mauricfo@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Return-path: Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:47831 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755449AbdDEQYI (ORCPT ); Wed, 5 Apr 2017 12:24:08 -0400 In-Reply-To: <1491405499-5429-1-git-send-email-mauricfo@linux.vnet.ibm.com> Content-Language: en-US Content-ID: <6AFBED30E2C4B2479E7D9BD46AB486A1@namprd15.prod.outlook.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Mauricio Faria de Oliveira Cc: "linux-scsi@vger.kernel.org" , "martin.petersen@oracle.com" , "dan.j.williams@intel.com" , "jejb@linux.vnet.ibm.com" , Jens Axboe , "hare@suse.de" , "hch@lst.de" , "gpiccoli@linux.vnet.ibm.com" > On Apr 5, 2017, at 8:18 AM, Mauricio Faria de Oliveira wrote: >=20 > The commit 08024885a2a3 ("ses: Add power_status to SES device slot") > introduced the 'power_status' attribute to enclosure components and > the associated callbacks. >=20 > There are 2 callbacks available to get the power status of a device: > 1) ses_get_power_status() for 'struct enclosure_component_callbacks' > 2) get_component_power_status() for the sysfs device attribute > (these are available for kernel-space and user-space, respectively.) >=20 > However, despite both methods being available to get power status > on demand, that commit also introduced a call to get power status > in ses_enclosure_data_process(). >=20 > This dramatically increased the total probe time for SCSI devices > on larger configurations, because ses_enclosure_data_process() is > called several times during the SCSI devices probe and loops over > the component devices (but that is another problem, another patch). >=20 > That results in a tremendous continuous hammering of SCSI Receive > Diagnostics commands to the enclosure-services device, which does > delay the total probe time for the SCSI devices __significantly__: >=20 > Originally, ~34 minutes on a system attached to ~170 disks: >=20 > [ 9214.490703] mpt3sas version 13.100.00.00 loaded > ... > [11256.580231] scsi 17:0:177:0: qdepth(16), tagged(1), simple(0), > ordered(0), scsi_level(6), cmd_que(1) >=20 > With this patch, it decreased to ~2.5 minutes -- a 13.6x faster >=20 > [ 1002.992533] mpt3sas version 13.100.00.00 loaded > ... > [ 1151.978831] scsi 11:0:177:0: qdepth(16), tagged(1), simple(0), > ordered(0), scsi_level(6), cmd_que(1) >=20 > Back to the commit discussion.. on the ses_get_power_status() call > introduced in ses_enclosure_data_process(): impact of removing it. >=20 > That may possibly be in place to initialize the power status value > on device probe. However, those 2 functions available to retrieve > that value _do_ automatically refresh/update it. So the potential > benefit would be a direct access of the 'power_status' field which > does not use the callbacks... >=20 > But the only reader of 'struct enclosure_component::power_status' > is the get_component_power_status() callback for sysfs attribute, > and it _does_ check for and call the .get_power_status callback, > (which indeed is defined and implemented by that commit), so the > power status value is, again, automatically updated. >=20 > So, the remaining potential for a direct/non-callback access to > the power_status attribute would be out-of-tree modules -- well, > for those, if they are for whatever reason interested in values > that are set during device probe and not up-to-date by the time > they need it.. well, that would be curious. >=20 > Well, to handle that more properly, set the initial power state > value to '-1' (i.e., uninitialized) instead of '1' (power 'on'), > and check for it in that callback which may do an direct access > to the field value _if_ a callback function is not defined. >=20 > Signed-off-by: Mauricio Faria de Oliveira > Fixes: 08024885a2a3 ("ses: Add power_status to SES device slot") > --- >=20 > v2: > - remove module parameter. > - better return values for -1/uninitalized power_status. > (thanks: Dan Williams ) >=20 > drivers/misc/enclosure.c | 7 ++++++- > drivers/scsi/ses.c | 1 - > 2 files changed, 6 insertions(+), 2 deletions(-) >=20 > diff --git a/drivers/misc/enclosure.c b/drivers/misc/enclosure.c > index 65fed7146e9b..d3fe3ea902d4 100644 > --- a/drivers/misc/enclosure.c > +++ b/drivers/misc/enclosure.c > @@ -148,7 +148,7 @@ struct enclosure_device * > for (i =3D 0; i < components; i++) { > edev->component[i].number =3D -1; > edev->component[i].slot =3D -1; > - edev->component[i].power_status =3D 1; > + edev->component[i].power_status =3D -1; > } >=20 > mutex_lock(&container_list_lock); > @@ -594,6 +594,11 @@ static ssize_t get_component_power_status(struct dev= ice *cdev, >=20 > if (edev->cb->get_power_status) > edev->cb->get_power_status(edev, ecomp); > + > + /* If still uninitialized, the callback failed or does not exist. */ > + if (ecomp->power_status =3D=3D -1) > + return (edev->cb->get_power_status) ? -EIO : -ENOTTY; > + > return snprintf(buf, 40, "%s\n", ecomp->power_status ? "on" : "off"); > } >=20 > diff --git a/drivers/scsi/ses.c b/drivers/scsi/ses.c > index 50adabbb5808..f1cdf32d7514 100644 > --- a/drivers/scsi/ses.c > +++ b/drivers/scsi/ses.c > @@ -548,7 +548,6 @@ static void ses_enclosure_data_process(struct enclosu= re_device *edev, > ecomp =3D &edev->component[components++]; >=20 > if (!IS_ERR(ecomp)) { > - ses_get_power_status(edev, ecomp); > if (addl_desc_ptr) > ses_process_descriptor( > ecomp, > --=20 > 1.8.3.1 >=20 Reviewed-by: Song Liu