On Wed, Mar 27, 2024 at 06:58:45PM -0700, Deepak Gupta via lists.riscv.org wrote:
On Tue, Mar 19, 2024 at 7:21 PM Samuel Holland
<samuel.holland@xxxxxxxxxx> wrote:
> else
> regs->status |= SR_UXL_64;
> #endif
> + current->thread_info.envcfg = ENVCFG_BASE;
> }
>
> And instead of context switching in `_switch_to`,
> In `entry.S` pick up `envcfg` from `thread_info` and write it into CSR.
The immediate reason is that writing envcfg in ret_from_exception() adds cycles
to every IRQ and system call exit, even though most of them will not change the
envcfg value. This is especially the case when returning from an IRQ/exception
back to S-mode, since envcfg has zero effect there.
A quick observation:
So I tried this on my setup. When I put `senvcfg` writes in
`__switch_to ` path, qemu suddenly
just tanks and takes a lot of time to boot up as opposed to when
`senvcfg` was in trap return path.
In my case entire userspace (all processes) have cfi enabled for them
via `senvcfg` and it gets
context switched. Not sure it's specific to my setup. I don't think it
should be an issue on actual
hardware.
Still debugging why it slows down my qemu drastically when same writes
to same CSR
are moved from `ret_from_exception` to `switch_to`
Nevermind and sorry for the bother. An issue on my setup.
-=-=-=-=-=-=-=-=-=-=-=-
Links: You receive all messages sent to this group.
View/Reply Online (#680): https://lists.riscv.org/g/tech-j-ext/message/680
Mute This Topic: https://lists.riscv.org/mt/105033914/7300952
Group Owner: tech-j-ext+owner@xxxxxxxxxxxxxxx
Unsubscribe: https://lists.riscv.org/g/tech-j-ext/unsub [debug@xxxxxxxxxxxx]
-=-=-=-=-=-=-=-=-=-=-=-
