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Re: bpf jit
>> Are there measurements supporting the idea that the BPF pcode engine
>> is a performance bottleneck?
> I didn't do any measurements myself of the whole system because I
> don't have access to any test [network] but jitted code is 3-5 times
> faster in my benchmark. In absolute values it's IIRC 30ns per packet
> on my amd64 and 150-200ns on my Tegra-250 arm.
Then it comes down to, is saving 30ns worh the code size and complexity
(and thus exposure)? I don't know how large a fraction of the cost of
packet handling 30ns is; I suspect it's small enough that I don't
consider it worth the costs. (To pick a number out of thin air, is
handling a packet in 970ns instead of 1us worth it? I think it's not,
and I suspect 1us to handle a packet is highly optimistic, though I
haven't measured that either.)
>> Particularly since it seems to me that the CPUs it supports are the
>> ones least in need of a performance boost?
> Mine supports several cpu types. Or do they all fall into "least in
> need of a performance boost"?
Most of them certainly do. The ones that most need a performance boost
are things like acorn26, sun2, hp300, vax, the slower pmax and
>> Compilers are, in general, full of subtle corner cases; jitters,
>> even more so.
> Why do you think that jitters are more full of subtle corner cases?
They've got most of the complexities of all compilers, plus a bunch
more all their own. It's uncomfortably close to "so complex there are
no obvious defects" rather than "so simple there are obviously no
>> And BPF is highly privileged, highly exposed, and security critical;
>> it seems to me that all the indications are against putting a jitter
> Yes, I'm aware it's highly exposed code but I'm not pushing it to
I'm not sure how that makes it any more appropriate to put it into the
main tree at this stage, but it doesn't really matter. I won't be
running -6 myself (for plenty of other reasons); I've pointed out my
concerns, and if NetBSD wants to ignore them, it's NetBSD's decision,
and NetBSD's security on the line.
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