Subject: Re: [next-queue 1/3] i40e: Store the irq number in i40e_q_vector

From: Joe Damato <[email-masked]>
Date: Wed, 5 Oct 2022 10:00:20 -0700

On Wed, Oct 05, 2022 at 12:29:24PM +0200, Maciej Fijalkowski wrote:
> On Wed, Oct 05, 2022 at 01:31:41AM -0700, Joe Damato wrote:
> > Make it easy to figure out the IRQ number for a particular i40e_q_vector by
> > storing the assigned IRQ in the structure itself.
> > 
> > Signed-off-by: Joe Damato <[email-masked]>
> > ---
> >  drivers/net/ethernet/intel/i40e/i40e.h      | 1 +
> >  drivers/net/ethernet/intel/i40e/i40e_main.c | 1 +
> >  2 files changed, 2 insertions(+)
> > 
> > diff --git a/drivers/net/ethernet/intel/i40e/i40e.h b/drivers/net/ethernet/intel/i40e/i40e.h
> > index 9926c4e..8e1f395 100644
> > --- a/drivers/net/ethernet/intel/i40e/i40e.h
> > +++ b/drivers/net/ethernet/intel/i40e/i40e.h
> > @@ -992,6 +992,7 @@ struct i40e_q_vector {
> >  	struct rcu_head rcu;	/* to avoid race with update stats on free */
> >  	char name[I40E_INT_NAME_STR_LEN];
> >  	bool arm_wb_state;
> > +	int irq_num;		/* IRQ assigned to this q_vector */
> 
> This struct looks like a mess in terms of members order. Can you check
> with pahole how your patch affects the layout of it? Maybe while at it you
> could pack it in a better way?

OK, sure. I used pahole and asked it to reorganize the struct members,
which saves 24 bytes.

I'll update this commit to include the following reorganization in the v2 of
this set:

$ pahole -R -C i40e_q_vector i40e.ko

struct i40e_q_vector {
	struct i40e_vsi *          vsi;                  /*     0     8 */
	u16                        v_idx;                /*     8     2 */
	u16                        reg_idx;              /*    10     2 */
	u8                         num_ringpairs;        /*    12     1 */
	u8                         itr_countdown;        /*    13     1 */
	bool                       arm_wb_state;         /*    14     1 */

	/* XXX 1 byte hole, try to pack */

	struct napi_struct         napi;                 /*    16   400 */
	/* --- cacheline 6 boundary (384 bytes) was 32 bytes ago --- */
	struct i40e_ring_container rx;                   /*   416    32 */
	/* --- cacheline 7 boundary (448 bytes) --- */
	struct i40e_ring_container tx;                   /*   448    32 */
	cpumask_t                  affinity_mask;        /*   480    24 */
	struct irq_affinity_notify affinity_notify;      /*   504    56 */
	/* --- cacheline 8 boundary (512 bytes) was 48 bytes ago --- */
	struct callback_head       rcu;                  /*   560    16 */
	/* --- cacheline 9 boundary (576 bytes) --- */
	char                       name[32];             /*   576    32 */

	/* XXX 4 bytes hole, try to pack */

	int                        irq_num;              /*   612     4 */

	/* size: 616, cachelines: 10, members: 14 */
	/* sum members: 611, holes: 2, sum holes: 5 */
	/* last cacheline: 40 bytes */
};   /* saved 24 bytes! */