netdev - Re: [PATCH net-next 0/5] skbuff: introduce skbuff

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Message-ID: <20210112110802.3914-1-alobakin@pm.me>
Date:   Tue, 12 Jan 2021 11:08:35 +0000
From:   Alexander Lobakin <alobakin@...me>
To:     Edward Cree <ecree.xilinx@...il.com>
Cc:     Alexander Lobakin <alobakin@...me>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Edward Cree <ecree@...arflare.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Guillaume Nault <gnault@...hat.com>,
        Yadu Kishore <kyk.segfault@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 0/5] skbuff: introduce skbuff_heads bulking and reusing

From: Edward Cree <ecree.xilinx@...il.com>
Date: Tue, 12 Jan 2021 09:54:04 +0000

> Without wishing to weigh in on whether this caching is a good idea...

Well, we already have a cache to bulk flush "consumed" skbs, although
kmem_cache_free() is generally lighter than kmem_cache_alloc(), and
a page frag cache to allocate skb->head that is also bulking the
operations, since it contains a (compound) page with the size of
min(SZ_32K, PAGE_SIZE).
If they wouldn't give any visible boosts, I think they wouldn't hit
mainline.

> Wouldn't it be simpler, rather than having two separate "alloc" and "flush"
>  caches, to have a single larger cache, such that whenever it becomes full
>  we bulk flush the top half, and when it's empty we bulk alloc the bottom
>  half?  That should mean fewer branches, fewer instructions etc. than
>  having to decide which cache to act upon every time.

I though about a unified cache, but couldn't decide whether to flush
or to allocate heads and how much to process. Your suggestion answers
these questions and generally seems great. I'll try that one, thanks!

> -ed

Al