[RFC PATCH v3] target/mips: Increase number of TLB entries on the 34Kf core (16 -> 64) - Philippe Mathieu-Daudé

From: "Philippe Mathieu-Daudé" <f4bug@amsat.org>
To: qemu-devel@nongnu.org, Victor Kamensky <kamensky@cisco.com>
Cc: "Aleksandar Rikalo" <aleksandar.rikalo@syrmia.com>,
	"Khem Raj" <raj.khem@gmail.com>,
	"Philippe Mathieu-Daudé" <f4bug@amsat.org>,
	"Richard Purdie" <richard.purdie@linuxfoundation.org>,
	"Aurelien Jarno" <aurelien@aurel32.net>,
	"Richard Henderson" <rth@twiddle.net>
Subject: [RFC PATCH v3] target/mips: Increase number of TLB entries on the 34Kf core (16 -> 64)
Date: Fri, 16 Oct 2020 15:33:17 +0200	[thread overview]
Message-ID: <20201016133317.553068-1-f4bug@amsat.org> (raw)

Per "MIPS32 34K Processor Core Family Software User's Manual,
Revision 01.13" page 8 in "Joint TLB (JTLB)" section:

  "The JTLB is a fully associative TLB cache containing 16, 32,
   or 64-dual-entries mapping up to 128 virtual pages to their
   corresponding physical addresses."

There is no particular reason to restrict the 34Kf core model to
16 TLB entries, so raise its config to 64.

This is helpful for other projects, in particular the Yocto Project:

  Yocto Project uses qemu-system-mips 34Kf cpu model, to run 32bit
  MIPS CI loop. It was observed that in this case CI test execution
  time was almost twice longer than 64bit MIPS variant that runs
  under MIPS64R2-generic model. It was investigated and concluded
  that the difference in number of TLBs 16 in 34Kf case vs 64 in
  MIPS64R2-generic is responsible for most of CI real time execution
  difference. Because with 16 TLBs linux user-land trashes TLB more
  and it needs to execute more instructions in TLB refill handler
  calls, as result it runs much longer.

(https://lists.gnu.org/archive/html/qemu-devel/2020-10/msg03428.html)

Buglink: https://bugzilla.yoctoproject.org/show_bug.cgi?id=13992
Reported-by: Victor Kamensky <kamensky@cisco.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
v3: KISS
Supersedes: <20201015224746.540027-1-f4bug@amsat.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 target/mips/translate_init.c.inc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/mips/translate_init.c.inc b/target/mips/translate_init.c.inc
index 637caccd890..ad21756f4d9 100644
--- a/target/mips/translate_init.c.inc
+++ b/target/mips/translate_init.c.inc
@@ -254,7 +254,7 @@ const mips_def_t mips_defs[] =
         .CP0_PRid = 0x00019500,
         .CP0_Config0 = MIPS_CONFIG0 | (0x1 << CP0C0_AR) |
                        (MMU_TYPE_R4000 << CP0C0_MT),
-        .CP0_Config1 = MIPS_CONFIG1 | (1 << CP0C1_FP) | (15 << CP0C1_MMU) |
+        .CP0_Config1 = MIPS_CONFIG1 | (1 << CP0C1_FP) | (63 << CP0C1_MMU) |
                        (0 << CP0C1_IS) | (3 << CP0C1_IL) | (1 << CP0C1_IA) |
                        (0 << CP0C1_DS) | (3 << CP0C1_DL) | (1 << CP0C1_DA) |
                        (1 << CP0C1_CA),
-- 
2.26.2


