Re: [PATCH v1 4/4] accel/tcg: increase default code gen buffer size for 64 bit

[Richard Henderson]

On 2/26/20 10:10 AM, Alex Bennée wrote:
> While 32mb is certainly usable a full system boot ends up flushing the
> codegen buffer nearly 100 times. Increase the default on 64 bit hosts
> to take advantage of all that spare memory. After this change I can
> boot my tests system without any TB flushes.

> +#if TCG_TARGET_REG_BITS == 32
>  #define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (32 * MiB)
> +#else
> +#define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (2 * GiB)
> +#endif

This particular number, I'm not so sure about.

It makes sense for a lone vm, running in system mode, on a large-ish host.
It's more questionable for a large-ish host running many system mode vm's,
although one can tune that from the command-line, so perhaps it's still ok.

It does not make sense for a linux-user chroot, running make -jN, on just about
any host.  For linux-user, I could be happy with a modest increase, but not all
the way out to 2GiB.

Discuss.


r~