linux-kernel - Re: Percpu variables, benchmarking, and performance weirdness

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Message-ID: <20191220163441.GH2914998@devbig004.ftw2.facebook.com>
Date:   Fri, 20 Dec 2019 08:34:41 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>,
        Björn Töpel <bjorn.topel@...il.com>,
        bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Christoph Lameter <cl@...ux.com>,
        Dennis Zhou <dennis@...nel.org>
Subject: Re: Percpu variables, benchmarking, and performance weirdness

On Fri, Dec 20, 2019 at 08:22:02AM -0800, Eric Dumazet wrote:
> I definitely seen expensive per-cpu updates in the stack.
> (SNMP counters, or per-cpu stats for packets/bytes counters)
> 
> It might be nice to have an option to use 2M pages.
> 
> (I recall sending some patches in the past about using high-order pages for vmalloc,
> but this went nowhere)

Yeah, the percpu allocator implementation is half-way prepared for
that.  There just hasn't been a real need for that yet.  If this
actually is a difference coming from tlb pressure, this might be it, I
guess?

Thanks.

-- 
tejun