From mboxrd@z Thu Jan 1 00:00:00 1970 From: guangrong.xiao@gmail.com Subject: [PATCH v3 0/5] mc146818rtc: fix Windows VM clock faster Date: Wed, 10 May 2017 16:32:54 +0800 Message-ID: <20170510083259.3900-1-xiaoguangrong@tencent.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, yunfangtai@tencent.com, Xiao Guangrong To: pbonzini@redhat.com, mst@redhat.com, mtosatti@redhat.com Return-path: Received: from mail-pg0-f53.google.com ([74.125.83.53]:36510 "EHLO mail-pg0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751081AbdEJIdS (ORCPT ); Wed, 10 May 2017 04:33:18 -0400 Received: by mail-pg0-f53.google.com with SMTP id 64so13070381pgb.3 for ; Wed, 10 May 2017 01:33:18 -0700 (PDT) Sender: kvm-owner@vger.kernel.org List-ID: From: Xiao Guangrong Changelog in v3: Thanks to Paolo's the elaborate review comments, this version simplifies the logic of periodic_timer_update() significantly that includes: 1) introduce rtc_periodic_clock_ticks() that takes both regA and regB into account and returns the period clock 2) count the clocks since last interrupt by always using current clock subtracts the clock when last interrupt happened 3) improve the assert() logic Paolo, all you comments have been reflected in this version except globally using s->period because in the current code, only x86 is using s->period so that we should obey this rule to keep compatible migration. I have added the comment to explain this suitable in the code: /* * as the old QEMUs only used s->period for the case that * LOST_TICK_POLICY_SLEW is used, in order to keep the * compatible migration, we obey the rule as old QEMUs. */ s->period = period; If anything i missed, please let me know. :) Changelog in v2: Thanks to Paolo's review, the changes in this version are: 1) merge patch 2, 3, 4 together 2) use a nice way ((value ^ new_value) & BIT_MASK) to check if updating for periodic timer is needed 3) use a smarter way to calculate coalesced irqs and lost_clock 4) make sure only x86 can enable LOST_TICK_POLICY_SLEW 5) make the code depends on LOST_TICK_POLICY_SLEW rather than TARGET_I386 We noticed that the clock on some windows VMs, e.g, Window7 and window8 is really faster and the issue can be easily reproduced by staring the VM with '-rtc base=localtime,clock=vm,driftfix=slew -no-hpet' and running attached code in the guest The root cause is that the clock will be lost if the periodic period is changed as currently code counts the next periodic time like this: next_irq_clock = (cur_clock & ~(period - 1)) + period; consider the case if cur_clock = 0x11FF and period = 0x100, then the next_irq_clock is 0x1200, however, there is only 1 clock left to trigger the next irq. Unfortunately, Windows guests (at least Windows7) change the period very frequently if it runs the attached code, so that the lost clock is accumulated, the wall-time become faster and faster The main idea to fix the issue is we use a accurate clock period to calculate the next irq: next_irq_clock = cur_clock + period; After that, it is really convenient to compensate clock if it is needed The code running in windows VM is attached: // TimeInternalTest.cpp : Defines the entry point for the console application. // #include "stdafx.h" #pragma comment(lib, "winmm") #include #include #define SWITCH_PEROID 13 int _tmain(int argc, _TCHAR* argv[]) { if (argc != 2) { printf("parameter error!\n"); printf("USAGE: *.exe time(ms)\n"); printf("example: *.exe 40\n"); return 0; } else { DWORD internal = atoi((char *)argv[1]); DWORD count = 0; while (1) { count++; timeBeginPeriod(1); DWORD start = timeGetTime(); Sleep(internal); timeEndPeriod(1); if ((count % SWITCH_PEROID) == 0) { Sleep(1); } } } return 0; } Tai Yunfang (1): mc146818rtc: precisely count the clock for periodic timer Xiao Guangrong (4): mc146818rtc: update periodic timer only if it is needed mc146818rtc: ensure LOST_TICK_POLICY_SLEW is only enabled on TARGET_I386 mc146818rtc: drop unnecessary '#ifdef TARGET_I386' mc146818rtc: embrace all x86 specific code hw/timer/mc146818rtc.c | 212 ++++++++++++++++++++++++++++++++++--------------- 1 file changed, 149 insertions(+), 63 deletions(-) -- 2.9.3 From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42841) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1d8N3l-0000ds-31 for qemu-devel@nongnu.org; Wed, 10 May 2017 04:33:26 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1d8N3f-0003gh-Ca for qemu-devel@nongnu.org; Wed, 10 May 2017 04:33:25 -0400 Received: from mail-pg0-x22d.google.com ([2607:f8b0:400e:c05::22d]:33788) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1d8N3f-0003gF-4s for qemu-devel@nongnu.org; Wed, 10 May 2017 04:33:19 -0400 Received: by mail-pg0-x22d.google.com with SMTP id u187so13063119pgb.0 for ; Wed, 10 May 2017 01:33:18 -0700 (PDT) From: guangrong.xiao@gmail.com Date: Wed, 10 May 2017 16:32:54 +0800 Message-Id: <20170510083259.3900-1-xiaoguangrong@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: [Qemu-devel] [PATCH v3 0/5] mc146818rtc: fix Windows VM clock faster List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: pbonzini@redhat.com, mst@redhat.com, mtosatti@redhat.com Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, yunfangtai@tencent.com, Xiao Guangrong From: Xiao Guangrong Changelog in v3: Thanks to Paolo's the elaborate review comments, this version simplifies the logic of periodic_timer_update() significantly that includes: 1) introduce rtc_periodic_clock_ticks() that takes both regA and regB into account and returns the period clock 2) count the clocks since last interrupt by always using current clock subtracts the clock when last interrupt happened 3) improve the assert() logic Paolo, all you comments have been reflected in this version except globally using s->period because in the current code, only x86 is using s->period so that we should obey this rule to keep compatible migration. I have added the comment to explain this suitable in the code: /* * as the old QEMUs only used s->period for the case that * LOST_TICK_POLICY_SLEW is used, in order to keep the * compatible migration, we obey the rule as old QEMUs. */ s->period = period; If anything i missed, please let me know. :) Changelog in v2: Thanks to Paolo's review, the changes in this version are: 1) merge patch 2, 3, 4 together 2) use a nice way ((value ^ new_value) & BIT_MASK) to check if updating for periodic timer is needed 3) use a smarter way to calculate coalesced irqs and lost_clock 4) make sure only x86 can enable LOST_TICK_POLICY_SLEW 5) make the code depends on LOST_TICK_POLICY_SLEW rather than TARGET_I386 We noticed that the clock on some windows VMs, e.g, Window7 and window8 is really faster and the issue can be easily reproduced by staring the VM with '-rtc base=localtime,clock=vm,driftfix=slew -no-hpet' and running attached code in the guest The root cause is that the clock will be lost if the periodic period is changed as currently code counts the next periodic time like this: next_irq_clock = (cur_clock & ~(period - 1)) + period; consider the case if cur_clock = 0x11FF and period = 0x100, then the next_irq_clock is 0x1200, however, there is only 1 clock left to trigger the next irq. Unfortunately, Windows guests (at least Windows7) change the period very frequently if it runs the attached code, so that the lost clock is accumulated, the wall-time become faster and faster The main idea to fix the issue is we use a accurate clock period to calculate the next irq: next_irq_clock = cur_clock + period; After that, it is really convenient to compensate clock if it is needed The code running in windows VM is attached: // TimeInternalTest.cpp : Defines the entry point for the console application. // #include "stdafx.h" #pragma comment(lib, "winmm") #include #include #define SWITCH_PEROID 13 int _tmain(int argc, _TCHAR* argv[]) { if (argc != 2) { printf("parameter error!\n"); printf("USAGE: *.exe time(ms)\n"); printf("example: *.exe 40\n"); return 0; } else { DWORD internal = atoi((char *)argv[1]); DWORD count = 0; while (1) { count++; timeBeginPeriod(1); DWORD start = timeGetTime(); Sleep(internal); timeEndPeriod(1); if ((count % SWITCH_PEROID) == 0) { Sleep(1); } } } return 0; } Tai Yunfang (1): mc146818rtc: precisely count the clock for periodic timer Xiao Guangrong (4): mc146818rtc: update periodic timer only if it is needed mc146818rtc: ensure LOST_TICK_POLICY_SLEW is only enabled on TARGET_I386 mc146818rtc: drop unnecessary '#ifdef TARGET_I386' mc146818rtc: embrace all x86 specific code hw/timer/mc146818rtc.c | 212 ++++++++++++++++++++++++++++++++++--------------- 1 file changed, 149 insertions(+), 63 deletions(-) -- 2.9.3