Re: [PATCH v2 0/3] tcg: Defer tb_flush when initial thread region alloc fails

On 8/18/26 10:07, Yogesh Vyas wrote:
> 
> Hi Richard,
> 
> On Sun, Aug 16, 2026 at 10:38 PM Yogesh Vyas <[email protected] 
> <mailto:[email protected]>> wrote:
> 
>     Hi Richard,
>     Thank you for improvising on the initial patch shared.
> 
>     On Thu, Aug 13, 2026 at 6:20 AM Richard Henderson <[email protected]
>     <mailto:[email protected]>> wrote:
> 
>         Hi Yogesh,
> 
>         The main problem with your patch is where you've placed the change:
>         tcg_region_initial_alloc__locked is also used by tcg_region_reset_all,
>         used by tb_flush.  Along that path, we really can't have a failure.
>         The path on which we can defer allocation is via tcg_register_thread.
> 
>         The second change I made is to use code_buf_ptr == NULL to signal
>         reallocation is required.  In addition, tcg_tb_alloc doesn't need
>         to immediately fail: in the interim since thread creation, we may
>         well have performed a tb_flush already.
> 
>         Please have a try vs your hotplug test case.
> 
>     I tried testing these patches on my x86 host running qemu-system-ppc64 by initially
>     hotpluging 400 vCPUs.
>     While the response was relatively slower than the initial patch that I had shared, I
>     also observed the VM is as slow as stuck when I retried hotplugging upto 1024.
>     I will share more feedback if I have any.
> 
> 
> I have shared one minor comment on patch 2/3, with that:
> 
> Reviewed-by: Yogesh Vyas <[email protected] <mailto:[email protected]>>
> Tested-by: Yogesh Vyas <[email protected] <mailto:[email protected]>>
Thanks.

r`