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Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_E
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register |
Date: |
Thu, 18 Aug 2016 10:50:30 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 |
On 18/08/2016 09:56, Vijay Kilari wrote:
> The get_aarch_cpu_id() has check " if (unlikely(!cpu_info_read)) ".
> If we call get_aarch_cpu_id() from is_thunderx_pass2_cpu() which is
> called from inside the loop, we will be adding one additional check.
On the other hand, you are making an assumption that the caller of
is_thunderx_pass2_cpu() calls get_aarch64_cpu_id() first, and not
documenting it anywhere.
And given that you shouldn't call _any_ function from inside such a hot
loop, your solution is inferior on both counts.
Paolo
> What I observed is having extra check inside the loop is adding 100 to
> 200ms overhead
> on live migration time. So I added this variable extra is_thunderx_cpu
> static variable
> to make it simple single check.
- [Qemu-devel] [RFC PATCH v2 0/2] Live migration optimization for Thunderx platform, vijay . kilari, 2016/08/16
- [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, vijay . kilari, 2016/08/16
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Paolo Bonzini, 2016/08/17
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Vijay Kilari, 2016/08/18
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register,
Paolo Bonzini <=
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Vijay Kilari, 2016/08/18
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Paolo Bonzini, 2016/08/18
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Richard Henderson, 2016/08/18
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Peter Maydell, 2016/08/18
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Richard Henderson, 2016/08/18
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Peter Maydell, 2016/08/18
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Vijay Kilari, 2016/08/19
- Re: [Qemu-devel] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register, Richard Henderson, 2016/08/19
[Qemu-devel] [RFC PATCH v2 2/2] utils: Add prefetch for Thunderx platform, vijay . kilari, 2016/08/16