netdev - Re: [PATCH net-next v4 4/6] enic: Use the Page Pool API for RX when MTU is less than page size

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Message-Id: <20250110235204.8536-1-johndale@cisco.com>
Date: Fri, 10 Jan 2025 15:52:04 -0800
From: John Daley <johndale@...co.com>
To: kuba@...nel.org
Cc: andrew+netdev@...n.ch,
	benve@...co.com,
	davem@...emloft.net,
	edumazet@...gle.com,
	johndale@...co.com,
	neescoba@...co.com,
	netdev@...r.kernel.org,
	pabeni@...hat.com,
	satishkh@...co.com
Subject: Re: [PATCH net-next v4 4/6] enic: Use the Page Pool API for RX when MTU is less than page size

On 1/4/25, 5:42 PM, "Jakub Kicinski" kuba@...nel.org wrote:

>On Thu,  2 Jan 2025 14:24:25 -0800 John Daley wrote:
>> The Page Pool API improves bandwidth and CPU overhead by recycling
>> pages instead of allocating new buffers in the driver. Make use of
>> page pool fragment allocation for smaller MTUs so that multiple
>> packets can share a page.
>
>Why the MTU limitation? You can set page_pool_params.order 
>to appropriate value always use the page pool.
>
>> Added 'pp_alloc_error' per RQ ethtool statistic to count
>> page_pool_dev_alloc() failures.
>
>SG, but please don't report it via ethtool. Add it in 
>enic_get_queue_stats_rx() as alloc_fail (and enic_get_base_stats()).
>As one of the benefits you'll be able to use
>tools/testing/selftests/drivers/net/hw/pp_alloc_fail.py
>to test this stat and error handling in the driver.

Fyi, after making suggested change I used pp_alloc_fail.py but no
errors were injected. I think the path from page_pool_dev_alloc()
does not call page_pool_alloc_pages()?

Here is what I beleive the call path is:
page_pool_dev_alloc(rq->pool, &offset, &truesize)
  page_pool_alloc(pool, offset, size, gfp)
    netmem_to_page(page_pool_alloc_netmem(pool, offset, size, gfp));
      page_pool_alloc_frag_netmem(pool, offset, *size, gfp);
        page_pool_alloc_netmems(pool, gfp);
          __page_pool_alloc_pages_slow(pool, gfp);

If I change the call from page_pool_dev_alloc() to
page_pool_dev_alloc_pages() in the driver I do see the errors injected.