RE: [PATCH V5,net-next] net: mana: Add page pool for RX buffers

[Haiyang Zhang]

> -----Original Message-----
> From: Jesper Dangaard Brouer <hawk@xxxxxxxxxx>
> Sent: Friday, August 4, 2023 6:50 AM
> To: Jesse Brandeburg <jesse.brandeburg@xxxxxxxxx>; Haiyang Zhang
> <haiyangz@xxxxxxxxxxxxx>; linux-hyperv@xxxxxxxxxxxxxxx;
> netdev@xxxxxxxxxxxxxxx
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> kernel@xxxxxxxxxxxxxxx; Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx>
> Subject: Re: [PATCH V5,net-next] net: mana: Add page pool for RX buffers
> 
> 
> 
> On 03/08/2023 03.44, Jesse Brandeburg wrote:
> > On 8/2/2023 11:07 AM, Haiyang Zhang wrote:
> >> Add page pool for RX buffers for faster buffer cycle and reduce CPU
> >> usage.
> >>
> 
> Can you add some info on the performance improvement this patch gives?
I will add this to the patch description.

> 
> Your previous post mentioned:
>  > With iperf and 128 threads test, this patch improved the throughput
> by 12-15%, and decreased the IRQ associated CPU's usage from 99-100% to
> 10-50%.
> 
> 
> >> The standard page pool API is used.
> >>
> >> Signed-off-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> >> ---
> >> V5:
> >> In err path, set page_pool_put_full_page(..., false) as suggested by
> >> Jakub Kicinski
> >> V4:
> >> Add nid setting, remove page_pool_nid_changed(), as suggested by
> >> Jesper Dangaard Brouer
> >> V3:
> >> Update xdp mem model, pool param, alloc as suggested by Jakub Kicinski
> >> V2:
> >> Use the standard page pool API as suggested by Jesper Dangaard Brouer
> >> ---
> >
> >> diff --git a/include/net/mana/mana.h b/include/net/mana/mana.h
> >> index 024ad8ddb27e..b12859511839 100644
> >> --- a/include/net/mana/mana.h
> >> +++ b/include/net/mana/mana.h
> >> @@ -280,6 +280,7 @@ struct mana_recv_buf_oob {
> >>   	struct gdma_wqe_request wqe_req;
> >>
> >>   	void *buf_va;
> >> +	bool from_pool; /* allocated from a page pool */
> >
> > suggest you use flags and not bools, as bools waste 7 bits each, plus
> > your packing of this struct will be full of holes, made worse by this
> > patch. (see pahole tool)
> >
> 
> Agreed.
Thanks, I will do this when adding more flags in future patches.

> 
> >
> >>
> >>   	/* SGL of the buffer going to be sent has part of the work request. */
> >>   	u32 num_sge;
> >> @@ -330,6 +331,8 @@ struct mana_rxq {
> >>   	bool xdp_flush;
> >>   	int xdp_rc; /* XDP redirect return code */
> >>
> >> +	struct page_pool *page_pool;
> >> +
> >>   	/* MUST BE THE LAST MEMBER:
> >>   	 * Each receive buffer has an associated mana_recv_buf_oob.
> >>   	 */
> >
> >
> > The rest of the patch looks ok and is remarkably compact for a
> > conversion to page pool. I'd prefer someone with more page pool exposure
> > review this for correctness, but FWIW
>  >
> 
> Both Jakub and I have reviewed the page_pool parts, and I think we are
> in a good place.
> 
> Looking at the driver, I wonder why you are keeping the driver local
> memory cache (when PP is also contains a memory cache) ?
> (I assume there is a good reason, so this is not blocking patch)

You mean the "else" part of the code below? It's for a compound page from
napi_alloc_frag(), not from the pool. If any error happens,  we save it
locally for re-use.

drop:
        if (from_pool) {
                page_pool_recycle_direct(rxq->page_pool,
                                         virt_to_head_page(buf_va));
        } else {
                WARN_ON_ONCE(rxq->xdp_save_va);
                /* Save for reuse */
                rxq->xdp_save_va = buf_va;
        }


> 
> >
> > Reviewed-by: Jesse Brandeburg <jesse.brandeburg@xxxxxxxxx>
> 
> Thanks for taking your time to review.
> 
> I'm ready to ACK once the description is improved a bit :-)
> 
> --Jesper
> pw-bot: cr