linux-kernel - Re: [RFC PATCH] drivers: hv: Convert open-coded timeouts to msecs_to

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Message-ID: <2dff61bd-55d8-430f-9d92-6cbfe1bf6326@linux.microsoft.com>
Date: Fri, 18 Oct 2024 15:49:54 -0700
From: Easwar Hariharan <eahariha@...ux.microsoft.com>
To: Praveen Kumar <kumarpraveen@...ux.microsoft.com>, lkp@...el.com,
 "K. Y. Srinivasan" <kys@...rosoft.com>,
 Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>,
 Dexuan Cui <decui@...rosoft.com>,
 "open list:Hyper-V/Azure CORE AND DRIVERS" <linux-hyperv@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>
Cc: eahariha@...ux.microsoft.com, Naman Jain <namjain@...ux.microsoft.com>,
 Shradha Gupta <shradhagupta@...ux.microsoft.com>
Subject: Re: [RFC PATCH] drivers: hv: Convert open-coded timeouts to
 msecs_to_jiffies()

On 10/18/2024 12:54 AM, Praveen Kumar wrote:
> On 17-10-2024 04:07, Easwar Hariharan wrote:
>> We have several places where timeouts are open-coded as N (seconds) * HZ,
>> but best practice is to use msecs_to_jiffies(). Convert the timeouts to
>> make them HZ invariant.
>>> Signed-off-by: Easwar Hariharan <eahariha@...ux.microsoft.com>
>> ---
>>  drivers/hv/hv_balloon.c  | 9 +++++----
>>  drivers/hv/hv_kvp.c      | 4 ++--
>>  drivers/hv/hv_snapshot.c | 6 ++++--
>>  drivers/hv/vmbus_drv.c   | 2 +-
>>  4 files changed, 12 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
>> index c38dcdfcb914d..3017d41f12681 100644
>> --- a/drivers/hv/hv_balloon.c
>> +++ b/drivers/hv/hv_balloon.c
>> @@ -756,7 +756,7 @@ static void hv_mem_hot_add(unsigned long start, unsigned long size,
>>  		 * adding succeeded, it is ok to proceed even if the memory was
>>  		 * not onlined in time.
>>  		 */
>> -		wait_for_completion_timeout(&dm_device.ol_waitevent, 5 * HZ);
>> +		wait_for_completion_timeout(&dm_device.ol_waitevent, msecs_to_jiffies(5 * 1000));
> 
> Is it correct to convert HZ to 1000 ?
> Also, how are you testing these changes ?
> 

It's a conversion of milliseconds to seconds, rather than HZ to 1000. :)
msecs_to_jiffies() handles the conversion to jiffies with HZ. As Naman
mentioned, this could be equivalently written as 5 * MSECS_PER_SEC, and
would probably be more readable. On testing, this is only
compile-tested, and that's part of the reason why it's an RFC, since I'm
not 100% sure every one of these timeouts is measured in seconds. Hoping
for folks more familiar with the code to take a look.

Thanks,
Easwar