[v4] Reinvent BQL-free PIO/MMIO

[PATCH v4 3/8] hpet: switch to fain-grained device locking

Igor Mammedov posted 8 patches 2 months, 2 weeks ago

Diff against v1 v2 v3
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Maintainers: Richard Henderson <richard.henderson@linaro.org>, Paolo Bonzini <pbonzini@redhat.com>, Riku Voipio <riku.voipio@iki.fi>, "Michael S. Tsirkin" <mst@redhat.com>, Igor Mammedov <imammedo@redhat.com>, Ani Sinha <anisinha@redhat.com>, Thomas Huth <thuth@redhat.com>, Halil Pasic <pasic@linux.ibm.com>, Christian Borntraeger <borntraeger@linux.ibm.com>, David Hildenbrand <david@redhat.com>, Jason Herne <jjherne@linux.ibm.com>, Stafford Horne <shorne@gmail.com>, Eduardo Habkost <eduardo@habkost.net>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, "Philippe Mathieu-Daudé" <philmd@linaro.org>, Yanan Wang <wangyanan55@huawei.com>, Zhao Liu <zhao1.liu@intel.com>, Peter Xu <peterx@redhat.com>, Peter Maydell <peter.maydell@linaro.org>, Alexander Graf <agraf@csgraf.de>, Mads Ynddal <mads@ynddal.dk>, Michael Rolnik <mrolnik@gmail.com>, Helge Deller <deller@gmx.de>, Cameron Esfahani <dirty@apple.com>, Roman Bolshakov <rbolshakov@ddn.com>, Phil Dennis-Jordan <phil@philjordan.eu>, Marcelo Tosatti <mtosatti@redhat.com>, Reinoud Zandijk <reinoud@netbsd.org>, Sunil Muthuswamy <sunilmut@microsoft.com>, Song Gao <gaosong@loongson.cn>, Laurent Vivier <laurent@vivier.eu>, "Edgar E. Iglesias" <edgar.iglesias@gmail.com>, Aurelien Jarno <aurelien@aurel32.net>, Jiaxun Yang <jiaxun.yang@flygoat.com>, Aleksandar Rikalo <arikalo@gmail.com>, Huacai Chen <chenhuacai@kernel.org>, Nicholas Piggin <npiggin@gmail.com>, Chinmay Rath <rathc@linux.ibm.com>, Harsh Prateek Bora <harshpb@linux.ibm.com>, Yoshinori Sato <yoshinori.sato@nifty.com>, Ilya Leoshkevich <iii@linux.ibm.com>, Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>, Artyom Tarasenko <atar4qemu@gmail.com>

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[PATCH v4 3/8] hpet: switch to fain-grained device locking

Posted by Igor Mammedov 2 months, 2 weeks ago

as a step towards lock-less HPET counter read,
use per device locking instead of BQL.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
---
 hw/timer/hpet.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/hw/timer/hpet.c b/hw/timer/hpet.c
index cb48cc151f..ab5aa59ae4 100644
--- a/hw/timer/hpet.c
+++ b/hw/timer/hpet.c
@@ -38,6 +38,7 @@
 #include "hw/timer/i8254.h"
 #include "system/address-spaces.h"
 #include "qom/object.h"
+#include "qemu/lockable.h"
 #include "trace.h"
 
 struct hpet_fw_config hpet_fw_cfg = {.count = UINT8_MAX};
@@ -69,6 +70,7 @@ struct HPETState {
     SysBusDevice parent_obj;
     /*< public >*/
 
+    QemuMutex lock;
     MemoryRegion iomem;
     uint64_t hpet_offset;
     bool hpet_offset_saved;
@@ -428,6 +430,7 @@ static uint64_t hpet_ram_read(void *opaque, hwaddr addr,
     trace_hpet_ram_read(addr);
     addr &= ~4;
 
+    QEMU_LOCK_GUARD(&s->lock);
     /*address range of all global regs*/
     if (addr <= 0xff) {
         switch (addr) {
@@ -482,6 +485,7 @@ static void hpet_ram_write(void *opaque, hwaddr addr,
     int len = MIN(size * 8, 64 - shift);
     uint64_t old_val, new_val, cleared;
 
+    QEMU_LOCK_GUARD(&s->lock);
     trace_hpet_ram_write(addr, value);
     addr &= ~4;
 
@@ -679,8 +683,10 @@ static void hpet_init(Object *obj)
     SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
     HPETState *s = HPET(obj);
 
+    qemu_mutex_init(&s->lock);
     /* HPET Area */
     memory_region_init_io(&s->iomem, obj, &hpet_ram_ops, s, "hpet", HPET_LEN);
+    memory_region_enable_lockless_io(&s->iomem);
     sysbus_init_mmio(sbd, &s->iomem);
 }
 
-- 
2.47.1

Re: [PATCH v4 3/8] hpet: switch to fain-grained device locking

Posted by Zhao Liu 2 months ago

On Thu, Aug 14, 2025 at 06:05:55PM +0200, Igor Mammedov wrote:
> Date: Thu, 14 Aug 2025 18:05:55 +0200
> From: Igor Mammedov <imammedo@redhat.com>
> Subject: [PATCH v4 3/8] hpet: switch to fain-grained device locking
> 
> as a step towards lock-less HPET counter read,
> use per device locking instead of BQL.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> Reviewed-by: Peter Xu <peterx@redhat.com>
> ---
>  hw/timer/hpet.c | 6 ++++++
>  1 file changed, 6 insertions(+)

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>