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Date:   Tue, 12 Jan 2021 14:05:27 +0800
From:   Shuo A Liu <>
To:     Davidlohr Bueso <>
Cc:     <>, <>,
        Greg Kroah-Hartman <>,
        "H . Peter Anvin" <>,
        "Thomas Gleixner" <>,
        Ingo Molnar <>,
        "Borislav Petkov" <>, Yu Wang <>,
        Reinette Chatre <>,
        Zhi Wang <>,
        Zhenyu Wang <>
Subject: Re: [PATCH v7 09/18] virt: acrn: Introduce I/O request management

On Mon 11.Jan'21 at 13:52:19 -0800, Davidlohr Bueso wrote:
>On Wed, 06 Jan 2021, wrote:
>>The processing flow of I/O requests are listed as following:
>>a) The I/O handler of the hypervisor will fill an I/O request with
>>  PENDING state when a trapped I/O access happens in a User VM.
>>b) The hypervisor makes an upcall, which is a notification interrupt, to
>>  the Service VM.
>>c) The upcall handler schedules a tasklet to dispatch I/O requests.
>>d) The tasklet looks for the PENDING I/O requests, assigns them to
>>  different registered clients based on the address of the I/O accesses,
>>  updates their state to PROCESSING, and notifies the corresponding
>>  client to handle.
>Hmm so tasklets are deprecated (and have been for a while) and it's sad
>to see incoming new users in modern Linux. This wouldn't be the first one,
>however. We should be _removing_ users, not adding... In addition, this
>expands the whole tasklet_disable/enable() hacks.

Sorry, i had not noticed that.

>Could this not be done in process context instead?

It could be. The original consideration with tasklet was more about
performance as the I/O requests dispatching is a hot code path. I think
irq thread has little performance impact? I can have a try to convert
the tasklet to irq thread.


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