From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46867) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cwSrX-00060K-B2 for qemu-devel@nongnu.org; Fri, 07 Apr 2017 08:19:36 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cwSrU-00023C-76 for qemu-devel@nongnu.org; Fri, 07 Apr 2017 08:19:35 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51352) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cwSrT-00021E-Ud for qemu-devel@nongnu.org; Fri, 07 Apr 2017 08:19:32 -0400 Date: Fri, 7 Apr 2017 08:19:28 -0400 (EDT) From: Paolo Bonzini Message-ID: <2061307774.11920398.1491567568031.JavaMail.zimbra@redhat.com> In-Reply-To: <87k26wa1ry.fsf@linaro.org> References: <20170405132503.32125-1-alex.bennee@linaro.org> <20170405132503.32125-12-alex.bennee@linaro.org> <5ee6d2cb-d3e5-8b28-6a73-2d84c44ce614@redhat.com> <87k26wa1ry.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v2 11/12] cpus: call cpu_update_icount on read List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alex =?utf-8?Q?Benn=C3=A9e?= Cc: dovgaluk@ispras.ru, rth@twiddle.net, peter maydell , qemu-devel@nongnu.org, mttcg@greensocs.com, fred konrad , a rigo , cota@braap.org, bobby prani , nikunj@linux.vnet.ibm.com, Peter Crosthwaite ----- Original Message ----- > From: "Alex Benn=C3=A9e" > To: "Paolo Bonzini" > Cc: dovgaluk@ispras.ru, rth@twiddle.net, "peter maydell" , qemu-devel@nongnu.org, > mttcg@greensocs.com, "fred konrad" , "a rigo" = , > cota@braap.org, "bobby prani" , nikunj@linux.vnet.= ibm.com, "Peter Crosthwaite" > > Sent: Friday, April 7, 2017 7:35:29 PM > Subject: Re: [PATCH v2 11/12] cpus: call cpu_update_icount on read >=20 >=20 > Paolo Bonzini writes: >=20 > > On 05/04/2017 15:25, Alex Benn=C3=A9e wrote: > >> This ensures each time the vCPU thread reads the icount we update the > >> master timer_state.qemu_icount field. This way as long as updates are > >> in BQL protected sections (which they should be) the main-loop can > >> never come to update the log and find time has gone backwards. > >> > >> Signed-off-by: Alex Benn=C3=A9e > >> --- > >> cpus.c | 6 ++---- > >> 1 file changed, 2 insertions(+), 4 deletions(-) > >> > >> diff --git a/cpus.c b/cpus.c > >> index ff75af449a..63de033cc8 100644 > >> --- a/cpus.c > >> +++ b/cpus.c > >> @@ -246,19 +246,17 @@ void cpu_update_icount(CPUState *cpu) > >> > >> int64_t cpu_get_icount_raw(void) > >> { > >> - int64_t icount; > >> CPUState *cpu =3D current_cpu; > >> > >> - icount =3D atomic_read(&timers_state.qemu_icount); > >> if (cpu && cpu->running) { > >> if (!cpu->can_do_io) { > >> fprintf(stderr, "Bad icount read\n"); > >> exit(1); > >> } > >> /* Take into account what has run */ > >> - icount +=3D cpu_get_icount_executed(cpu); > >> + cpu_update_icount(cpu); > >> } > >> - return icount; > >> + return atomic_read(&timers_state.qemu_icount); > >> } > >> > >> /* Return the virtual CPU time, based on the instruction counter. */ > >> > > > > Maybe the update should be done in gen_io_start instead. There > > shouldn't be any interference between vCPU and I/O threads except > > between gen_io_start and gen_io_end. >=20 > I'm not sure I follow. gen_io_start is a translation time thing. At > least here we ensure we update whenever the value is read. Sorry, I meant we should generate TCG opcodes for the translation in gen_io_start. Paolo