From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 8C36E193418; Mon, 21 Oct 2024 03:41:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729482105; cv=none; b=b7de/6iOJR2FDI7x/CDVe/RrmYvx3Jyctp6AZHqrhPqjVazI7SfJfSP1iiQDv5h8P9wij6SpbPd/fFnSTAIwOQ5lwACaaPPfhRJuFxQJzu/fIedQ0+bc5/ROzJpegy5Qr51dzUUMLdcEPCFVKkTASPoPBKl73dvbWimLUtPT6kY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729482105; c=relaxed/simple; bh=gfWm/4z4crplHnbiNFIJoycUa8MJ5HnTjbTzsu6yYaA=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=oK2vkbH9b5b4hDOH4esl35CsaMzNR1UCEEx1aW/aQplCtxpcgLc4zgUz7sehFqbjbIe8vC+m1NBYgF6nNoCLyat9aGAZhoubCIjzu4o9ko1m0QkoN2YCHK/5Q2T2IZ+mBjfRW0NIZI3H4RjXvUQzB5/IvsJCQ0t2aUG2z3BbCjw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=j8/XsvqU; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="j8/XsvqU" Received: from [192.168.35.166] (c-73-118-245-227.hsd1.wa.comcast.net [73.118.245.227]) by linux.microsoft.com (Postfix) with ESMTPSA id BE88E210B2C1; Sun, 20 Oct 2024 20:41:42 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com BE88E210B2C1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1729482103; bh=FpzeBHnxnwvm83aCWDE4wDZb+brbprUE31r+txIYr9Q=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=j8/XsvqUSa3KtQ7u04BoG9ATeEVWesk5EMN/BA7gG8Poejcxw6fe0b0dkJyi/02rG JthCOlW66I5UzIpQue1v+Z6qfyCCamTbZhaKb+5OcoIuf4YfJJde+JiAzwvS1jOIeZ rr1dtPlM7KVuqEJM8n0ARyV+Cl2bb2ZjuWX7ydnE= Message-ID: <61f0eb38-2f0d-4f0f-a90c-18a02ebf4c55@linux.microsoft.com> Date: Sun, 20 Oct 2024 20:41:42 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: eahariha@linux.microsoft.com, Naman Jain , Shradha Gupta Subject: Re: [RFC PATCH] drivers: hv: Convert open-coded timeouts to msecs_to_jiffies() To: Michael Kelley , Praveen Kumar , "lkp@intel.com" , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , "open list:Hyper-V/Azure CORE AND DRIVERS" , open list References: <20241016223730.531861-1-eahariha@linux.microsoft.com> <9f4baf14-8182-451d-9849-4326a783d5c1@linux.microsoft.com> <2dff61bd-55d8-430f-9d92-6cbfe1bf6326@linux.microsoft.com> Content-Language: en-US From: Easwar Hariharan In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/18/2024 9:59 PM, Michael Kelley wrote: > From: Easwar Hariharan Sent: Friday, October 18, 2024 3:50 PM >> >> 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 >>>> --- >>>> 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. >> > > I believe the current code is correct. Two things: > > 1) The values multiplied by HZ are indeed in seconds. The number of > seconds are somewhat arbitrary in some of the cases, so you might > argue for a different number of seconds. But as coded, the values > are in seconds. Thanks for reviewing, Michael, and for the confirmation. > > 2) Unless I'm missing something, the current code uses the correct > timeout regardless of the value of HZ because the number of jiffies > per second *is* HZ. > > As such, it might help to be explicit in the commit message that this > patch isn't fixing any bugs. Will do. > As the commit message says, the patch is > to bring the code into conformance with best practices. I presume > the best practice you reference is described in > Documentation/scheduler/completion.rst. > > I don't understand the statement about making the code "HZ invariant", > which I think came from the aforementioned documentation. Per > my #2 above, I think the existing code is already "HZ invariant", at > least for how I would interpret "HZ invariant". > That's right, both the best practice and the statement of HZ-invariance came from the scheduler documentation you pointed out. While I can't find the source with a quick search right now, I understand that HZ varies with CPU frequency and I figure that's what the statement is referring to. Unfortunately, there wasn't any discussion on HZ-invariance I can find on the lore thread where the statement was added. [1] It seems to be one of those "it's so self explanatory it doesn't warrant a mention" unless you're one of today's 10,000. [2] [1] https://lore.kernel.org/all/1539183392-239389-1-git-send-email-john.garry@huawei.com/T/#u [2] https://xkcd.com/1053/ > Regardless of the meaning of "HZ invariant", I agree with the idea of > eliminating the use of HZ in cases like this, and letting msecs_to_jiffies() > handle it. Unfortunately, converting from "5 * HZ" to > "msecs_to_jiffies(5 * 1000)" makes the code really clunky. I would > advocate for adding something like this to include/linux/jiffies.h: > > #define secs_to_jiffies(secs) msecs_to_jiffies((secs) * 1000) > > and then using secs_to_jiffies() for all the cases in this patch. That > reduces the clunkiness. But maybe somebody in the past tried to > add secs_to_jiffies() and got shot down -- I don't know. It seems like > an obvious thing to add .... > > Michael >From a quick search on lore with dfb:secs_to_jiffies, it doesn't look like anyone has tried to add secs_to_jiffies() to jiffies.h. There is one instance of secs_to_jiffies() being defined in net/bluetooth/hci_event.c, added in 2021. Thanks, Easwar