From: Aurelien Jarno <aurelien@aurel32.net>
To: Richard Henderson <rth@twiddle.net>
Cc: peter.maydell@linaro.org, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v4 25/26] tcg: Check for overflow via highwater mark
Date: Wed, 30 Sep 2015 18:50:31 +0200 [thread overview]
Message-ID: <20150930165031.GD17449@aurel32.net> (raw)
In-Reply-To: <1443589786-26929-26-git-send-email-rth@twiddle.net>
On 2015-09-30 15:09, Richard Henderson wrote:
> We currently pre-compute an worst case code size for any TB, which
> works out to be 122kB. Since the average TB size is near 1kB, this
> wastes quite a lot of storage.
The code generation buffer is currently computed as 1/4 of the guest
RAM in softmmu mode (so 32MB for the default 128MB of RAM) or 32MB in
user mode. 122kB is therefore less than 0.4% of waster memory, I am not
therefore sure we need to add so much code just for that.
BTW, I wonder if it is really a good idea to scale the code generation
buffer with the size of the RAM, as the two do not seem that related. It
happens that at some point we don't really increases performances
anymore, and always defining it as 32MB might actually be a good idea.
Personally I am using a patch that limits it to 128MB.
--
Aurelien Jarno GPG: 4096R/1DDD8C9B
aurelien@aurel32.net http://www.aurel32.net
next prev parent reply other threads:[~2015-09-30 16:51 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-30 5:09 [Qemu-devel] [PATCH v4 00/26] Do away with TB retranslation Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 01/26] tcg: Rename debug_insn_start to insn_start Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 02/26] target-*: Unconditionally emit tcg_gen_insn_start Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 03/26] target-*: Increment num_insns immediately after tcg_gen_insn_start Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 04/26] target-*: Introduce and use cpu_breakpoint_test Richard Henderson
2015-09-30 15:27 ` Aurelien Jarno
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 05/26] tcg: Allow extra data to be attached to insn_start Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 06/26] target-arm: Add condexec state " Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 07/26] target-i386: Add cc_op " Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 08/26] target-mips: Add delayed branch " Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 09/26] target-s390x: Add cc_op " Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 10/26] target-sh4: Add flags " Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 11/26] target-cris: Mirror gen_opc_pc into insn_start Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 12/26] target-sparc: Tidy gen_branch_a interface Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 13/26] target-sparc: Split out gen_branch_n Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 14/26] target-sparc: Remove gen_opc_jump_pc Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 15/26] target-sparc: Add npc state to insn_start Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 16/26] tcg: Merge cpu_gen_code into tb_gen_code Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 17/26] target-*: Drop cpu_gen_code define Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 18/26] tcg: Add TCG_MAX_INSNS Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 19/26] tcg: Pass data argument to restore_state_to_opc Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 20/26] tcg: Save insn data and use it in cpu_restore_state_from_tb Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 21/26] tcg: Remove gen_intermediate_code_pc Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 22/26] tcg: Remove tcg_gen_code_search_pc Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 23/26] tcg: Emit prologue to the beginning of code_gen_buffer Richard Henderson
2015-09-30 16:17 ` Aurelien Jarno
2015-09-30 20:20 ` Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 24/26] tcg: Allocate a guard page after code_gen_buffer Richard Henderson
2015-09-30 16:33 ` Aurelien Jarno
2015-09-30 20:01 ` Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 25/26] tcg: Check for overflow via highwater mark Richard Henderson
2015-09-30 16:50 ` Aurelien Jarno [this message]
2015-09-30 17:09 ` Peter Maydell
2015-09-30 20:11 ` Richard Henderson
2015-09-30 5:09 ` [Qemu-devel] [PATCH v4 26/26] tcg: Adjust CODE_GEN_AVG_BLOCK_SIZE Richard Henderson
2015-09-30 16:50 ` Aurelien Jarno
2015-09-30 18:42 ` [Qemu-devel] [PATCH v4 00/26] Do away with TB retranslation Aurelien Jarno
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