Commit 228cf793 authored by Konstantin Ozerkov's avatar Konstantin Ozerkov Committed by Takashi Iwai
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ALSA: intel8x0: Improve performance in virtual environment 



v3: detection code is x86 and KVM specific, hide it under ifdef
v2: add detection for virtual environments (KVM and Parallels)

This patch is intended to improve performance in virtualized environments
like Parallels Desktop or KVM/VirtualBox/QEMU (virtual ICH/AC97 audio).

I/O access is very time-expensive operation in virtual world: VCPU
can be rescheduled and in the worst case we get more than 10ms delay on
each I/O access.

In the virtual environment loop exit rule
(old_civ == current_civ && old_picb == current_picb) is never satisfied,
because old_picb is never the same as current_picb due to delay inspired
by reading current_civ. As a result loop ended by timeout and we get 10x
more I/O operations.

Experimental data from Prallels Desktop 7, RHEL6 guest (I/O ops per
second):

Original code:
In Port    Counter         Callback
   f014      41550         fffff00000179d00 ac97_bm_read_civ+0x000
   f018      41387         fffff0000017a580 ac97_bm_read_picb+0x000

With patch:
In Port    Counter         Callback
   f014       4090         fffff00000179d00 ac97_bm_read_civ+0x000
   f018       1964         fffff0000017a580 ac97_bm_read_picb+0x000

Signed-off-by: default avatarKonstantin Ozerkov <kozerkov@parallels.com>
Signed-off-by: default avatarDenis V. Lunev <den@openvz.org>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent c09403dc

sound/pci/intel8x0.c

+27 −2
Original line number Diff line number Diff line
@@ -42,6 +42,12 @@ 
#include <asm/pgtable.h>

#include <asm/cacheflush.h>



#ifdef CONFIG_KVM_GUEST

#include <asm/kvm_para.h>

#else

#define kvm_para_available() (0)

#endif



MODULE_AUTHOR("Jaroslav Kysela <perex@perex.cz>");

MODULE_DESCRIPTION("Intel 82801AA,82901AB,i810,i820,i830,i840,i845,MX440; SiS 7012; Ali 5455");

MODULE_LICENSE("GPL");
@@ -77,6 +83,7 @@ static int buggy_semaphore; 
static int buggy_irq = -1; /* auto-check */

static int xbox;

static int spdif_aclink = -1;

static int inside_vm = -1;



module_param(index, int, 0444);

MODULE_PARM_DESC(index, "Index value for Intel i8x0 soundcard.");
@@ -94,6 +101,8 @@ module_param(xbox, bool, 0444); 
MODULE_PARM_DESC(xbox, "Set to 1 for Xbox, if you have problems with the AC'97 codec detection.");

module_param(spdif_aclink, int, 0444);

MODULE_PARM_DESC(spdif_aclink, "S/PDIF over AC-link.");

module_param(inside_vm, bool, 0444);

MODULE_PARM_DESC(inside_vm, "KVM/Parallels optimization.");



/* just for backward compatibility */

static int enable;
@@ -400,6 +409,7 @@ struct intel8x0 { 
	unsigned buggy_irq: 1;		/* workaround for buggy mobos */

	unsigned xbox: 1;		/* workaround for Xbox AC'97 detection */

	unsigned buggy_semaphore: 1;	/* workaround for buggy codec semaphore */

	unsigned inside_vm: 1;		/* enable VM optimization */



	int spdif_idx;	/* SPDIF BAR index; *_SPBAR or -1 if use PCMOUT */

	unsigned int sdm_saved;	/* SDM reg value */
@@ -1065,8 +1075,11 @@ static snd_pcm_uframes_t snd_intel8x0_pcm_pointer(struct snd_pcm_substream *subs 
			udelay(10);

			continue;

		}

		if (civ == igetbyte(chip, ichdev->reg_offset + ICH_REG_OFF_CIV) &&

		    ptr1 == igetword(chip, ichdev->reg_offset + ichdev->roff_picb))

		if (civ != igetbyte(chip, ichdev->reg_offset + ICH_REG_OFF_CIV))

			continue;

		if (chip->inside_vm)

			break;

		if (ptr1 == igetword(chip, ichdev->reg_offset + ichdev->roff_picb))

			break;

	} while (timeout--);

	ptr = ichdev->last_pos;
@@ -2984,6 +2997,10 @@ static int __devinit snd_intel8x0_create(struct snd_card *card, 
	if (xbox)

		chip->xbox = 1;



	chip->inside_vm = inside_vm;

	if (inside_vm)

		printk(KERN_INFO "intel8x0: enable KVM optimization\n");



	if (pci->vendor == PCI_VENDOR_ID_INTEL &&

	    pci->device == PCI_DEVICE_ID_INTEL_440MX)

		chip->fix_nocache = 1; /* enable workaround */
@@ -3226,6 +3243,14 @@ static int __devinit snd_intel8x0_probe(struct pci_dev *pci, 
			buggy_irq = 0;

	}



	if (inside_vm < 0) {

		/* detect KVM and Parallels virtual environments */

		inside_vm = kvm_para_available();

#if defined(__i386__) || defined(__x86_64__)

		inside_vm = inside_vm || boot_cpu_has(X86_FEATURE_HYPERVISOR);

#endif

	}



	if ((err = snd_intel8x0_create(card, pci, pci_id->driver_data,

				       &chip)) < 0) {

		snd_card_free(card);

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