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Date:   Wed, 3 Jun 2020 15:54:09 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@redhat.com>
To:     Giovanni Cabiddu <giovanni.cabiddu@intel.com>
cc:     Mike Snitzer <msnitzer@redhat.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Milan Broz <mbroz@redhat.com>, djeffery@redhat.com,
        dm-devel@redhat.com, qat-linux@intel.com,
        linux-crypto@vger.kernel.org, guazhang@redhat.com,
        jpittman@redhat.com, ahsan.atta@intel.com
Subject: Re: [PATCH 1/4] qat: fix misunderstood -EBUSY return code
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On Wed, 3 Jun 2020, Giovanni Cabiddu wrote:

> > > > +bool adf_should_back_off(struct adf_etr_ring_data *ring)
> > > > +{
> > > > +	return atomic_read(ring->inflights) > ADF_MAX_INFLIGHTS(ring->ring_size, ring->msg_size) * 15 / 16;
> > > How did you came up with 15/16?
> > 
> > I want the sender to back off before the queue is full, to avoid 
> > busy-waiting. There may be more concurrent senders, so we want to back off 
> > at some point before the queue is full.
> Yes, I understood this. My question was about the actual number.
> 93% of the depth of the queue.

I just guessed the value. If you have some benchmark, you can try 
different values, to test if they perform better.

Mikulas