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Re: [Qemu-devel] [4352] Make sure we flush cached blocks from the tb-jmp
From: |
Fabrice Bellard |
Subject: |
Re: [Qemu-devel] [4352] Make sure we flush cached blocks from the tb-jmp-cache when we replace valid tlb entries . |
Date: |
Sat, 24 May 2008 01:31:21 +0200 |
User-agent: |
Thunderbird 1.5.0.9 (X11/20070212) |
Please revert this patch: it has a major performance hit because the
tb_jmp_cache is flushed too often. Flushing the tb_jmp_cache when
overriding a tlb_cache entry is not necessary, provided a given virtual
address is always remapped at the same physical address with the same
rights, which is the assumed API here. Detecting possible
inconsistencies is useful, but I am sure there is a solution without
such a performance hit.
Please avoid doing such modifications without doing regressions tests on
performance (e.g. a compilation with gcc).
Regards,
Fabrice.
Edgar E. Iglesias wrote:
> Revision: 4352
> http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=4352
> Author: edgar_igl
> Date: 2008-05-06 08:44:21 +0000 (Tue, 06 May 2008)
>
> Log Message:
> -----------
> Make sure we flush cached blocks from the tb-jmp-cache when we replace valid
> tlb entries.
>
> Modified Paths:
> --------------
> trunk/exec.c
>
> Modified: trunk/exec.c
> ===================================================================
> --- trunk/exec.c 2008-05-06 08:38:22 UTC (rev 4351)
> +++ trunk/exec.c 2008-05-06 08:44:21 UTC (rev 4352)
> @@ -1366,6 +1366,21 @@
>
> #if !defined(CONFIG_USER_ONLY)
>
> +static inline void tlb_flush_jmp_cache(CPUState *env, target_ulong addr)
> +{
> + unsigned int i;
> +
> + /* Discard jump cache entries for any tb which might potentially
> + overlap the flushed page. */
> + i = tb_jmp_cache_hash_page(addr - TARGET_PAGE_SIZE);
> + memset (&env->tb_jmp_cache[i], 0,
> + TB_JMP_PAGE_SIZE * sizeof(TranslationBlock *));
> +
> + i = tb_jmp_cache_hash_page(addr);
> + memset (&env->tb_jmp_cache[i], 0,
> + TB_JMP_PAGE_SIZE * sizeof(TranslationBlock *));
> +}
> +
> /* NOTE: if flush_global is true, also flush global entries (not
> implemented yet) */
> void tlb_flush(CPUState *env, int flush_global)
> @@ -1428,7 +1443,6 @@
> void tlb_flush_page(CPUState *env, target_ulong addr)
> {
> int i;
> - TranslationBlock *tb;
>
> #if defined(DEBUG_TLB)
> printf("tlb_flush_page: " TARGET_FMT_lx "\n", addr);
> @@ -1448,14 +1462,8 @@
> #endif
> #endif
>
> - /* Discard jump cache entries for any tb which might potentially
> - overlap the flushed page. */
> - i = tb_jmp_cache_hash_page(addr - TARGET_PAGE_SIZE);
> - memset (&env->tb_jmp_cache[i], 0, TB_JMP_PAGE_SIZE * sizeof(tb));
> + tlb_flush_jmp_cache(env, addr);
>
> - i = tb_jmp_cache_hash_page(addr);
> - memset (&env->tb_jmp_cache[i], 0, TB_JMP_PAGE_SIZE * sizeof(tb));
> -
> #if !defined(CONFIG_SOFTMMU)
> if (addr < MMAP_AREA_END)
> munmap((void *)addr, TARGET_PAGE_SIZE);
> @@ -1706,6 +1714,10 @@
> } else {
> te->addr_read = -1;
> }
> +
> + if (te->addr_code != -1) {
> + tlb_flush_jmp_cache(env, te->addr_code);
> + }
> if (prot & PAGE_EXEC) {
> te->addr_code = address;
> } else {
>
>
>
>
>