On Tue, Nov 05, 2019 at 07:11:04PM +0300, Denis Plotnikov wrote: > Linux guests submit IO requests no longer than PAGE_SIZE * max_seg > field reported by SCSI controler. Thus typical sequential read with > 1 MB size results in the following pattern of the IO from the guest: > 8,16 1 15754 2.766095122 2071 D R 2095104 + 1008 [dd] > 8,16 1 15755 2.766108785 2071 D R 2096112 + 1008 [dd] > 8,16 1 15756 2.766113486 2071 D R 2097120 + 32 [dd] > 8,16 1 15757 2.767668961 0 C R 2095104 + 1008 [0] > 8,16 1 15758 2.768534315 0 C R 2096112 + 1008 [0] > 8,16 1 15759 2.768539782 0 C R 2097120 + 32 [0] > The IO was generated by > dd if=/dev/sda of=/dev/null bs=1024 iflag=direct > > This effectively means that on rotational disks we will observe 3 IOPS > for each 2 MBs processed. This definitely negatively affects both > guest and host IO performance. > > The cure is relatively simple - we should report lengthy scatter-gather > ability of the SCSI controller. Fortunately the situation here is very > good. VirtIO transport layer can accomodate 1024 items in one request > while we are using only 128. This situation is present since almost > very beginning. 2 items are dedicated for request metadata thus we > should publish VIRTQUEUE_MAX_SIZE - 2 as max_seg. > > The following pattern is observed after the patch: > 8,16 1 9921 2.662721340 2063 D R 2095104 + 1024 [dd] > 8,16 1 9922 2.662737585 2063 D R 2096128 + 1024 [dd] > 8,16 1 9923 2.665188167 0 C R 2095104 + 1024 [0] > 8,16 1 9924 2.665198777 0 C R 2096128 + 1024 [0] > which is much better. > > To fix this particular case, the patch adds new machine types with > extended virtqueue sizes to 256 which also increases max_seg to 254 > implicitly. > > Suggested-by: Denis V. Lunev <d...@openvz.org> > Signed-off-by: Denis Plotnikov <dplotni...@virtuozzo.com> > ---
the way we normally do this is change the defaults to 256. what is wrong with doing that? > hw/core/machine.c | 14 ++++++++++++++ > hw/i386/pc_piix.c | 16 +++++++++++++--- > hw/i386/pc_q35.c | 14 ++++++++++++-- > include/hw/boards.h | 6 ++++++ > 4 files changed, 45 insertions(+), 5 deletions(-) > > diff --git a/hw/core/machine.c b/hw/core/machine.c > index 55b08f1466..28013a0e3f 100644 > --- a/hw/core/machine.c > +++ b/hw/core/machine.c > @@ -24,6 +24,13 @@ > #include "hw/pci/pci.h" > #include "hw/mem/nvdimm.h" > > +GlobalProperty hw_compat_4_0_1[] = { > + { "virtio-blk-device", "queue-size", "128" }, > + { "virtio-scsi-device", "virtqueue_size", "128" }, > + { "vhost-scsi-device", "virtqueue_size", "128" }, > +}; > +const size_t hw_compat_4_0_1_len = G_N_ELEMENTS(hw_compat_4_0_1); > + > GlobalProperty hw_compat_4_0[] = { > { "virtio-balloon-device", "qemu-4-0-config-size", "true" }, > }; > @@ -157,6 +164,13 @@ GlobalProperty hw_compat_2_1[] = { > }; > const size_t hw_compat_2_1_len = G_N_ELEMENTS(hw_compat_2_1); > > +GlobalProperty hw_compat[] = { > + { "virtio-blk-device", "queue-size", "256" }, > + { "virtio-scsi-device", "virtqueue_size", "256" }, > + { "vhost-scsi-device", "virtqueue_size", "256" }, > +}; > +const size_t hw_compat_len = G_N_ELEMENTS(hw_compat); > + > static char *machine_get_accel(Object *obj, Error **errp) > { > MachineState *ms = MACHINE(obj); > diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c > index 8ad8e885c6..2260a61b1b 100644 > --- a/hw/i386/pc_piix.c > +++ b/hw/i386/pc_piix.c > @@ -426,15 +426,27 @@ static void pc_i440fx_machine_options(MachineClass *m) > m->default_machine_opts = "firmware=bios-256k.bin"; > m->default_display = "std"; > machine_class_allow_dynamic_sysbus_dev(m, TYPE_RAMFB_DEVICE); > + compat_props_add(m->compat_props, hw_compat, hw_compat_len); > } > > -static void pc_i440fx_4_0_machine_options(MachineClass *m) > +static void pc_i440fx_4_0_2_machine_options(MachineClass *m) > { > pc_i440fx_machine_options(m); > m->alias = "pc"; > m->is_default = 1; > } > > +DEFINE_I440FX_MACHINE(v4_0_2, "pc-i440fx-4.0.2", NULL, > + pc_i440fx_4_0_2_machine_options); > + > +static void pc_i440fx_4_0_machine_options(MachineClass *m) > +{ > + pc_i440fx_4_0_2_machine_options(m); > + m->alias = NULL; > + m->is_default = 0; > + compat_props_add(m->compat_props, hw_compat_4_0_1, hw_compat_4_0_1_len); > +} > + > DEFINE_I440FX_MACHINE(v4_0, "pc-i440fx-4.0", NULL, > pc_i440fx_4_0_machine_options); > > @@ -443,9 +455,7 @@ static void pc_i440fx_3_1_machine_options(MachineClass *m) > PCMachineClass *pcmc = PC_MACHINE_CLASS(m); > > pc_i440fx_4_0_machine_options(m); > - m->is_default = 0; > m->smbus_no_migration_support = true; > - m->alias = NULL; > pcmc->pvh_enabled = false; > compat_props_add(m->compat_props, hw_compat_3_1, hw_compat_3_1_len); > compat_props_add(m->compat_props, pc_compat_3_1, pc_compat_3_1_len); > diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c > index 45cc29d1ad..50ccd9ebcf 100644 > --- a/hw/i386/pc_q35.c > +++ b/hw/i386/pc_q35.c > @@ -363,14 +363,25 @@ static void pc_q35_machine_options(MachineClass *m) > machine_class_allow_dynamic_sysbus_dev(m, TYPE_INTEL_IOMMU_DEVICE); > machine_class_allow_dynamic_sysbus_dev(m, TYPE_RAMFB_DEVICE); > m->max_cpus = 288; > + compat_props_add(m->compat_props, hw_compat, hw_compat_len); > } > > -static void pc_q35_4_0_1_machine_options(MachineClass *m) > +static void pc_q35_4_0_2_machine_options(MachineClass *m) > { > pc_q35_machine_options(m); > m->alias = "q35"; > } > > +DEFINE_Q35_MACHINE(v4_0_2, "pc-q35-4.0.2", NULL, > + pc_q35_4_0_2_machine_options); > + > +static void pc_q35_4_0_1_machine_options(MachineClass *m) > +{ > + pc_q35_4_0_2_machine_options(m); > + m->alias = NULL; > + compat_props_add(m->compat_props, hw_compat_4_0_1, hw_compat_4_0_1_len); > +} > + > DEFINE_Q35_MACHINE(v4_0_1, "pc-q35-4.0.1", NULL, > pc_q35_4_0_1_machine_options); > > @@ -378,7 +389,6 @@ static void pc_q35_4_0_machine_options(MachineClass *m) > { > pc_q35_4_0_1_machine_options(m); > m->default_kernel_irqchip_split = true; > - m->alias = NULL; > compat_props_add(m->compat_props, hw_compat_4_0, hw_compat_4_0_len); > compat_props_add(m->compat_props, pc_compat_4_0, pc_compat_4_0_len); > } > diff --git a/include/hw/boards.h b/include/hw/boards.h > index fe1885cbff..cf10632dac 100644 > --- a/include/hw/boards.h > +++ b/include/hw/boards.h > @@ -293,6 +293,9 @@ struct MachineState { > } \ > type_init(machine_initfn##_register_types) > > +extern GlobalProperty hw_compat_4_0_1[]; > +extern const size_t hw_compat_4_0_1_len; > + > extern GlobalProperty hw_compat_4_0[]; > extern const size_t hw_compat_4_0_len; > > @@ -338,4 +341,7 @@ extern const size_t hw_compat_2_2_len; > extern GlobalProperty hw_compat_2_1[]; > extern const size_t hw_compat_2_1_len; > > +extern GlobalProperty hw_compat[]; > +extern const size_t hw_compat_len; > + > #endif > -- > 2.17.0