netdev - Re: [PATCH net-next 05/15] ice: replace custom AIM algorithm with kernel's DIM library

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Message-ID: <20210415094651.06041834@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Thu, 15 Apr 2021 09:46:51 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Tony Nguyen <anthony.l.nguyen@...el.com>
Cc:     davem@...emloft.net, Jacob Keller <jacob.e.keller@...el.com>,
        netdev@...r.kernel.org, sassmann@...hat.com,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Brelinski <tonyx.brelinski@...el.com>
Subject: Re: [PATCH net-next 05/15] ice: replace custom AIM algorithm with
 kernel's DIM library

On Wed, 14 Apr 2021 17:30:03 -0700 Tony Nguyen wrote:
> +static void ice_tx_dim_work(struct work_struct *work)
> +{
> +	struct ice_ring_container *rc;
> +	struct ice_q_vector *q_vector;
> +	struct dim *dim;
> +	u16 itr, intrl;
> +
> +	dim = container_of(work, struct dim, work);
> +	rc = container_of(dim, struct ice_ring_container, dim);
> +	q_vector = container_of(rc, struct ice_q_vector, tx);
> +
> +	if (dim->profile_ix >= ARRAY_SIZE(tx_profile))
> +		dim->profile_ix = ARRAY_SIZE(tx_profile) - 1;
> +
> +	/* look up the values in our local table */
> +	itr = tx_profile[dim->profile_ix].itr;
> +	intrl = tx_profile[dim->profile_ix].intrl;
> +
> +	ice_write_itr(rc, itr);
> +	ice_write_intrl(q_vector, intrl);
> +
> +	dim->state = DIM_START_MEASURE;

Are you only doing register writes in ice_write_itr/intrl or talk to FW?
Scheduler is expensive so you can save real cycles if you don't have to
rely on a work to do the programming (not sure how hard that is with
DIM, but since you're already sorta poking at the internals I thought
I'd ask).