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Re: [Qemu-devel] RFC: Code fetch optimisation
From: |
Paul Brook |
Subject: |
Re: [Qemu-devel] RFC: Code fetch optimisation |
Date: |
Mon, 15 Oct 2007 03:30:55 +0100 |
User-agent: |
KMail/1.9.7 |
On Sunday 14 October 2007, J. Mayer wrote:
> Here's an updated version of the code fetch optimisation patch against
> current CVS.
> As a remainder, this patch avoid use of softmmu helpers to fetch the
> code in most case. A new target define TARGET_HAS_VLE_INSNS has been
> added which is used to handle the case of an instruction that span 2
> pages, when the target CPU uses a variable-length instructions encoding.
> For pure RISC, the code fetch is done using raw access routines.
> + unsigned long phys_pc;
> + unsigned long phys_pc_start;
These are ram offsets, not physical addresses. I recommend naming them as such
to avoid confusion.
> + opc = glue(glue(lds,SUFFIX),MEMSUFFIX)(virt_pc);
> + /* Avoid softmmu access on next load */
> + /* XXX: dont: phys PC is not correct anymore
> + * We could call get_phys_addr_code(env, pc); and remove the else
> + * condition, here.
> + */
> + //*start_pc = phys_pc;
The commented out code is completely bogus, please remove it. The comment is
also somewhat misleading/incorrect. The else would still be required for
accesses that span a page boundary.
The code itself looks ok, though I'd be surprised if it made a significant
difference. We're always going to hit the fast-path TLB lookup case anyway.
Paul
- [Qemu-devel] RFC: Code fetch optimisation, J. Mayer, 2007/10/12
- [Qemu-devel] RFC: Code fetch optimisation, J. Mayer, 2007/10/14
- Re: [Qemu-devel] RFC: Code fetch optimisation,
Paul Brook <=
- Re: [Qemu-devel] RFC: Code fetch optimisation, J. Mayer, 2007/10/15
- Re: [Qemu-devel] RFC: Code fetch optimisation, Paul Brook, 2007/10/15
- Re: [Qemu-devel] RFC: Code fetch optimisation, Fabrice Bellard, 2007/10/15
- Re: [Qemu-devel] RFC: Code fetch optimisation, J. Mayer, 2007/10/15
- Re: [Qemu-devel] RFC: Code fetch optimisation, Paul Brook, 2007/10/15
- Re: [Qemu-devel] RFC: Code fetch optimisation, J. Mayer, 2007/10/16
- Re: [Qemu-devel] RFC: Code fetch optimisation, Paul Brook, 2007/10/16
- Re: [Qemu-devel] RFC: Code fetch optimisation, J. Mayer, 2007/10/16
- Re: [Qemu-devel] RFC: Code fetch optimisation, Paul Brook, 2007/10/16
- Re: [Qemu-devel] RFC: Code fetch optimisation, Paul Brook, 2007/10/16