netdev - Re: [PATCH bpf-next 3/7] bpf: improve verification speed by not remarking live

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Date:   Fri, 29 Mar 2019 20:12:59 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Alexei Starovoitov <ast@...nel.org>
Cc:     <davem@...emloft.net>, <daniel@...earbox.net>, <jannh@...gle.com>,
        <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        <kernel-team@...com>
Subject: Re: [PATCH bpf-next 3/7] bpf: improve verification speed by not
 remarking live_read

On Fri, 29 Mar 2019 17:16:08 -0700, Alexei Starovoitov wrote:
> With large verifier speed improvement brought by the previous patch
> mark_reg_read() becomes the hottest function during verification.
> On a typical program it consumes 40% of cpu.
> mark_reg_read() walks parentage chain of registers to mark parents as LIVE_READ.
> Once the register is marked there is no need to remark it again in the future.
> Hence stop walking the chain once first LIVE_READ is seen.
> This optimization drops mark_reg_read() time from 40% of cpu to <1%
> and overall 2x improvement of verification speed.
> For some programs the longest_mark_read_walk counter improves from ~500 to ~5
> 
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>

Reviewed-by: Jakub Kicinski <jakub.kicinski@...ronome.com>