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From: | Alex Bennée |
Subject: | Re: [Qemu-devel] [PATCH v7 26/27] tcg: enable MTTCG by default for ARM on x86 hosts |
Date: | Fri, 20 Jan 2017 10:53:35 +0000 |
User-agent: | mu4e 0.9.19; emacs 25.1.91.2 |
Pranith Kumar <address@hidden> writes: > Alex Bennée writes: > >> This enables the multi-threaded system emulation by default for ARMv7 >> and ARMv8 guests using the x86_64 TCG backend. This is because on the >> guest side: >> >> - The ARM translate.c/translate-64.c have been converted to >> - use MTTCG safe atomic primitives >> - emit the appropriate barrier ops >> - The ARM machine has been updated to >> - hold the BQL when modifying shared cross-vCPU state >> - defer cpu_reset to async safe work >> >> All the host backends support the barrier and atomic primitives but >> need to provide same-or-better support for normal load/store >> operations. >> >> Signed-off-by: Alex Bennée <address@hidden> > > <snip> > >> >> +/* This defines the natural memory order supported by this >> + * architecture before guarantees made by various barrier >> + * instructions. >> + * >> + * The x86 has a pretty strong memory ordering which only really >> + * allows for some stores to be re-ordered after loads. >> + */ >> +#include "tcg-mo.h" >> + >> +static inline int get_tcg_target_mo(void) >> +{ >> + return TCG_MO_ALL & ~TCG_MO_LD_ST; >> +} >> + > > Shouldn't this be TCG_MO_ALL & ~TCG_MO_ST_LD? The case that x86 doesn't handle normally is store-after-load which is what I assumed TCG_MO_LD_ST was. Perhaps we need some better comments for each of the enums? > > Thanks, -- Alex Bennée
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