From: Richard Henderson <richard.henderson@linaro.org>
To: Bruno Piazera Larsen <bruno.larsen@eldorado.org.br>,
qemu-devel@nongnu.org
Cc: farosas@linux.ibm.com, luis.pires@eldorado.org.br,
Greg Kurz <groug@kaod.org>,
lucas.araujo@eldorado.org.br, fernando.valle@eldorado.org.br,
qemu-ppc@nongnu.org, matheus.ferst@eldorado.org.br,
david@gibson.dropbear.id.au
Subject: Re: [RFC PATCH] target/ppc: fix address translation bug for hash table mmus
Date: Mon, 7 Jun 2021 14:06:26 -0700 [thread overview]
Message-ID: <7198ccf1-f2db-2e39-3778-4083b5d7fa45@linaro.org> (raw)
In-Reply-To: <c79e73b0-f989-575b-0982-672fc9b289eb@eldorado.org.br>
On 6/7/21 12:29 PM, Bruno Piazera Larsen wrote:
> I just tried sending mmu_idx all the way down, but I ran into a very weird bug
> of gcc. If we have to add one more parameter that GCC can't just optimize away
> we get at least a slow down of 5x for the first test of check-acceptance (could
> be more, but the test times out after 900 seconds, so I'm not sure).
That's odd. We already have more arguments than the number of argument
registers... A 5x slowdown is distinctly odd.
> One way
> that I managed to get around that is saving the current MSR, setting it to 5,
> and restoring after the xlate call. The code ended up something like:
>
> int new_idx = (5<<HFLAGS_IMMU_IDX) | (5<<HFLAGS_DMMU_IDX);
> int clr = (7<<HFLAGS_IMMU_IDX) | (7<<HFLAGS_DMMU_IDX);
> int old_idx = env->msr & clr;
> clr = ~clr;
> /* set new msr so we don't need to send the mmu_idx */
> env->msr = (env->msr & clr) | new_idx;
> ret = ppc_radix64_partition_scoped_xlate(...);
> /* restore old mmu_idx */
> env->msr = (env->msr & clr) | old_idx;
No, this is silly.
We need to do one of two things:
- make sure everything is inlined,
- reduce the number of arguments.
We're currently passing in 9 arguments, which really is too many already. We
should be using something akin to mmu_ctx_t, but probably specific to radix64
without the random stuff collected for random other mmu models.
r~
next prev parent reply other threads:[~2021-06-07 21:07 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-02 19:18 [RFC PATCH] target/ppc: fix address translation bug for hash table mmus Bruno Larsen (billionai)
2021-06-02 19:26 ` Richard Henderson
2021-06-02 19:58 ` Bruno Piazera Larsen
2021-06-02 22:19 ` Richard Henderson
2021-06-07 19:29 ` Bruno Piazera Larsen
2021-06-07 21:06 ` Richard Henderson [this message]
2021-06-08 14:39 ` Bruno Piazera Larsen
2021-06-08 15:35 ` Richard Henderson
2021-06-08 16:37 ` Bruno Piazera Larsen
2021-06-08 18:39 ` Bruno Piazera Larsen
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