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Re: [Qemu-devel] [PATCH] target/arm: Convert ARM_TBFLAG_* to FIELDs

From: Alex Bennée
Subject: Re: [Qemu-devel] [PATCH] target/arm: Convert ARM_TBFLAG_* to FIELDs
Date: Tue, 18 Dec 2018 15:46:35 +0000
User-agent: mu4e 1.1.0; emacs 26.1.90

Richard Henderson <address@hidden> writes:

> On 12/17/18 9:43 AM, Alex Bennée wrote:
>>> Use "register" TBFLAG_ANY to indicate shared state between
>>> A32 and A64, and "registers" TBFLAG_A32 & TBFLAG_A64 for
>>> fields that are specific to the given cpu state.
>>> Move ARM_TBFLAG_BE to shared state, instead of its current
>>> placement within "Bit usage when in AArch32 state".
>> This looks like a worthwhile clean-up but really we need to defer this
>> calculation. It's in the top 2 hot functions on my build load stressor:
>>    5.74%  qemu-system-aarch64      [.] helper_lookup_tb_ptr
>>    5.05%  qemu-system-aarch64      [.] get_phys_addr_lpae
>>    4.39%  qemu-system-aarch64      [.] cpu_get_tb_cpu_state
>>    3.73%  qemu-system-aarch64      [.] tcg_gen_code
>>    3.65%  qemu-system-aarch64      [.] qht_lookup_custom
> Yes, I know.  We need to put on our thinking caps and come up with a scheme
> that minimizes the chances of missing an update to any (partially) 
> pre-computed
> value.
> That has been Peter's (legitimate) resistance to such a scheme so far.  There
> are a *lot* of variables that go into computing tb->flags.
> In the meantime this patch just makes the task of adding bits less
> ugly.

I'm having all sorts of trouble applying this patch - have you got a
commit I can reference?

Alex Bennée

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