From: Bart Van Assche <bvanassche@acm.org>
To: Guenter Roeck <linux@roeck-us.net>
Cc: linux-hwmon@vger.kernel.org, Jean Delvare <jdelvare@suse.com>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org,
Chris Healy <cphealy@gmail.com>,
Linus Walleij <linus.walleij@linaro.org>
Subject: Re: [PATCH 1/1] hwmon: Driver for temperature sensors on SATA drives
Date: Tue, 10 Dec 2019 11:10:33 -0500 [thread overview]
Message-ID: <ad33d8cb-5247-0bf8-d0cb-87073a41e3ff@acm.org> (raw)
In-Reply-To: <20191209192048.GA3940@roeck-us.net>
On 12/9/19 2:20 PM, Guenter Roeck wrote:
> On Mon, Dec 09, 2019 at 09:08:13AM -0800, Bart Van Assche wrote:
>> How much does synchronously submitting SCSI commands from inside the
>> device probing call back slow down SCSI device discovery? What is the
>> impact of this code on systems with a large number of ATA devices?
>
> Interesting question. In general, any SCSI commands would only be executed
> for SATA drives since the very first check in satatemp_identify() uses
> sdev->inquiriy and aborts if the drive in question is not an ATA drive.
> When connected to SATA drives, I measured the execution time of
> satatemp_identify() to be between ~900 uS and 1,700 uS on a system with
> Ryzen 3900 CPU.
>
> In more detail:
> - Time to read VPD page: ~10-20 uS
> - Time to execute SMART_READ_LOG/SCT_STATUS_REQ_ADDR: ~140-150 uS
> - Time to execute SMART_WRITE_LOG/SCT_STATUS_REQ_ADDR: ~600-1,500 uS
> - Time to execute SMART_READ_LOG/SCT_READ_LOG_ADDR: ~100-130 uS
>
> Does that answer your question ?
>
> Please note that I think that this is irrelevant in this context.
> The driver is only instantiated if loaded explicitly, so whoever uses it
> will be in a position to decide if the benefit of using it will outweigh
> its cost.
>
> If instantiation time ever becomes a real problem, for example if someone
> with a large number of SATA drives in a system wants to use the driver
> and is concerned about instantiation time, we can make the second part
> of its registration (ie everything after identifying SATA drives)
> asynchronous. That would, however, add a substantial amount of complexity
> to the driver, and we should only do it if it is really warranted.
Hi Guenter,
Thank you for having answered my question in great detail. I think this
overhead is low enough to be acceptable.
Bart.
next prev parent reply other threads:[~2019-12-10 16:10 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-09 5:21 [PATCH 0/1] Summary: hwmon driver for temperature sensors on SATA drives Guenter Roeck
2019-12-09 5:21 ` [PATCH 1/1] hwmon: Driver " Guenter Roeck
2019-12-09 5:28 ` Randy Dunlap
2019-12-09 6:00 ` Guenter Roeck
2019-12-09 17:08 ` Bart Van Assche
2019-12-09 19:20 ` Guenter Roeck
2019-12-10 16:10 ` Bart Van Assche [this message]
2019-12-12 22:33 ` Linus Walleij
2019-12-12 23:21 ` Martin K. Petersen
2019-12-13 4:18 ` Guenter Roeck
2019-12-17 2:47 ` Martin K. Petersen
2019-12-17 4:20 ` Guenter Roeck
2019-12-18 3:39 ` Martin K. Petersen
2019-12-11 4:08 ` [PATCH 0/1] Summary: hwmon driver " Martin K. Petersen
2019-12-11 5:57 ` Guenter Roeck
2019-12-17 2:35 ` Martin K. Petersen
2019-12-17 3:57 ` Guenter Roeck
2019-12-17 5:50 ` Damien Le Moal
2019-12-17 15:47 ` Guenter Roeck
2019-12-18 3:42 ` Martin K. Petersen
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