Re: [PATCH v2 1/6] linux-user/aarch64: Extend PR_SET_TAGGED_ADDR_CTRL for FEAT_MTE3

[Richard Henderson]

On 2/7/24 00:23, Peter Maydell wrote:
> On Tue, 6 Feb 2024 at 03:06, Richard Henderson
> <richard.henderson@linaro.org> wrote:
> > When MTE3 is supported, the kernel maps
> >    PR_MTE_TCF_ASYNC | PR_MTE_TCF_SYNC
> > to
> >    MTE_CTRL_TCF_ASYMM
> > and from there to
> >    SCTLR_EL1.TCF0 = 3
>
> This depends on the setting of
> /sys/devices/system/cpu/cpu<N>/mte_tcf_preferred :
> I think you only get asymm here if the sysadmin has set
> mte_tcf_preferred to 'asymm'; the default is 'async'.

Hmm, I missed that somewhere in the rat's nest.
I suspect this is over-engineered, such that no one will understand how to use 
it.

> For QEMU's implementation, are there any particular
> performance differences between sync, async and asymm ?

I doubt it.  Getting to the error path at all is the bulk of the work.

I think "performance" in this case would be highly test-case-centric.
Does the test "perform better" with async, which would allow the entire vector operation 
to finish in one go?

I suspect that for debugging purposes, sync is always preferred.
That might be the best setting for qemu.


r~