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Date:   Wed, 18 May 2022 18:29:03 +0800
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Subject: Re: [PATCH 1/2] psi: add support for multi level pressure stall
 trigger
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To:     Chen Wandun <chenwandun@huawei.com>,
        Suren Baghdasaryan <surenb@google.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Alex Shi <alexs@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>
References: <20220516033524.3130816-1-chenwandun@huawei.com>
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 <3a31521f-a68a-b2a9-baae-9a458ee17033@huawei.com>
From:   Alex Shi <seakeel@gmail.com>
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On 5/17/22 20:46, Chen Wandun wrote:
>>>> This breaks the old ABI. And why you need this new function?
>>> Both great points.
>> BTW, I think the additional max_threshold parameter could be
>> implemented in a backward compatible way so that the old API is not
>> broken:
>>
>> arg_count = sscanf(buf, "some %u %u %u", &min_threshold_us,  &arg2, &arg3);
>> if (arg_count < 2) return ERR_PTR(-EINVAL);
>> if (arg_count < 3) {
>>      max_threshold_us = INT_MAX;
>>      window_us = arg2;
>> } else {
>>      max_threshold_us = arg2;
>>      window_us = arg3;
>> }
> OK
> 
> Thanks.
>> But again, the motivation still needs to be explained.
> we want do different operation for different stall level,
> just as prev email explain, multi trigger is also OK in old
> ways, but it is a litter complex.

In fact, I am not keen for this solution, the older and newer
interface is easy to be confused by users, for some resolvable
unclear issues. It's not a good idea.

Thanks
Alex