linux-kernel - RE: [PATCH] zsmalloc: do not use bit_spin

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Message-ID: <0777a34e3e9246fe83e693ba07405d28@AcuMS.aculab.com>
Date:   Tue, 22 Dec 2020 09:20:12 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Song Bao Hua (Barry Song)'" <song.bao.hua@...ilicon.com>,
        Shakeel Butt <shakeelb@...gle.com>
CC:     Vitaly Wool <vitaly.wool@...sulko.com>,
        Minchan Kim <minchan@...nel.org>,
        Mike Galbraith <efault@....de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        NitinGupta <ngupta@...are.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: RE: [PATCH] zsmalloc: do not use bit_spin_lock

From: Song Bao Hua
> Sent: 21 December 2020 23:02
...
> > For decompression, I would like as low latency as possible which I
> > think is only possible by doing decompression on a cpu synchronously.
> 
> One possibility is that we change HW accelerator driver to be sync
> polling for decompression. But this still depends on async api as
> this is the framework nowadays, the difference would be the driver
> won't really block. crypto_wait_req() will return without actual
> sleep.

How long does the HW accelerated compress/decompress need to be before
it is actually worth sleeping the process?
While the HW version might be faster than the SW one, it may not be
enough faster to allow for the hardware interrupt and process sleep.
So it may be worth just spinning (polling the hardware register)
until the request completes.

If decompress are done that way, but compress left async, then
the decompress might need to fallback to SW if the HW is busy.

	David

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