linux-kernel - Re: [PATCH v5 2/3] crypto: engine - support for parallel requests based on retry mechanism

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Date:   Fri, 24 Apr 2020 14:34:57 +0000
From:   Iuliana Prodan <iuliana.prodan@....com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
CC:     Baolin Wang <baolin.wang@...aro.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Corentin Labbe <clabbe.montjoie@...il.com>,
        Horia Geanta <horia.geanta@....com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Maxime Ripard <mripard@...nel.org>,
        Aymen Sghaier <aymen.sghaier@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Silvano Di Ninno <silvano.dininno@....com>,
        Franck Lenormand <franck.lenormand@....com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH v5 2/3] crypto: engine - support for parallel requests
 based on retry mechanism

On 4/23/2020 2:47 PM, Herbert Xu wrote:
> On Wed, Apr 15, 2020 at 11:26:14PM +0300, Iuliana Prodan wrote:
>> Added support for executing multiple requests, in parallel,
>> for crypto engine based on a retry mechanism.
>> If hardware was unable to execute a backlog request, enqueue it
>> back in front of crypto-engine queue, to keep the order
>> of requests.
>>
>> A new variable is added, retry_support (this is to keep the
>> backward compatibility of crypto-engine) , which keeps track
>> whether the hardware has support for retry mechanism and,
>> also, if can run multiple requests.
>>
>> If do_one_request() returns:
>>> = 0: hardware executed the request successfully;
>> < 0: this is the old error path. If hardware has support for retry
>> mechanism, the request is put back in front of crypto-engine queue.
>> For backwards compatibility, if the retry support is not available,
>> the crypto-engine will work as before.
>> Only MAY_BACKLOG requests are enqueued back into
>> crypto-engine's queue, since the others can be dropped.
> 
> This looks a lot nicer!
> 
> However, I do have one little issue with the error case.  I think
> we should not lump all errors together.  For queueing errors, we
> should requeue regardless of MAY_BACKLOG.  After all, we don't
> want to have random packet loss just becayse the queue was full.
> 
> For other errors (e.g., a kmalloc error), we should requeue the
> MAY_BACKLOG requests and drop everythin else.
> 

Do you refer to the error codes returned by do_one_request (which sends 
the req to hw for execution)?

If this returns:
1. 0, success;
2. -ENOSPC, I'll requeue it regardless of MAY_BACKLOG;
3. any other error (-EIO, -EINVAL, -ENOMEM, etc), I'll requeue only 
MAY_BACKLOG requests.

Thanks,
Iulia