Dexuan Cui <decui@xxxxxxxxxxxxx> writes: >> -----Original Message----- >> From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx] >> Sent: Tuesday, April 21, 2015 22:28 >> To: KY Srinivasan >> Cc: Haiyang Zhang; devel@xxxxxxxxxxxxxxxxxxxxxx; linux- >> kernel@xxxxxxxxxxxxxxx; Dexuan Cui >> Subject: [PATCH 5/6] Drivers: hv: vmbus: distribute subchannels among all >> vcpus >> >> Primary channels are distributed evenly across all vcpus we have. When the >> host asks us to create subchannels it usually makes us num_cpus-1 offers > > Hi Vitaly, > AFAIK, in the VSP of storvsc, the number of subchannel is > (the_number_of_vcpus - 1) / 4. > > This means for a 8-vCPU guest, there is only 1 subchannel. > > Your new algorithm tends to make the vCPUs with small-number busier: > e.g., in the 8-vCPU case, assuming we have 4 SCSI controllers: > vCPU0: scsi0's PrimaryChannel (P) > vCPU1: scsi0's SubChannel (S) + scsi1's P > vCPU2: scsi1's S + scsi2's P > vCPU3: scsi2's S + scsi3's P > vCPU4: scsi3's S > vCPU5, 6 and 7 are idle. > > In this special case, the existing algorithm is better. :-) > > However, I do like this idea in your patch, that is, making sure a device's > primary/sub channels are assigned to differents vCPUs. Under special circumstances with the current code we can end up with having all subchannels on the same vCPU with the primary channel I guess :-) This is not something common, but possible. > > I'm just wondering if we should use an even better (and complex) > algorithm :-) The question here is - does sticking to the current vCPU help? If it does, I can suggest the following (I think I even mentioned that in my PATCH 00): first we try to find a (sub)channel with target_cpu == current_vcpu and only when we fail we do the round robin. I'd like to hear K.Y.'s opinion here as he's the original author :-) > > PS, yeah, for netvsc(HV_NIC_GUID), the number of SC is indeed > the_number_vcpus -1. I'm not sure about the upcoming HV_ND_GUID -- > maybe it's the same as HV_NIC_GUID. > > Thanks, > -- Dexuan > >> and we are supposed to distribute the work evenly among the channel >> itself and all its subchannels. Make sure they are all assigned to >> different vcpus. >> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> >> --- >> drivers/hv/channel_mgmt.c | 29 ++++++++++++++++++++++++++++- >> 1 file changed, 28 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c >> index 8f2761f..daa6417 100644 >> --- a/drivers/hv/channel_mgmt.c >> +++ b/drivers/hv/channel_mgmt.c >> @@ -270,6 +270,8 @@ static void init_vp_index(struct vmbus_channel >> *channel, >> int i; >> bool perf_chn = false; >> u32 max_cpus = num_online_cpus(); >> + struct vmbus_channel *primary = channel->primary_channel, *prev; >> + unsigned long flags; >> >> for (i = IDE; i < MAX_PERF_CHN; i++) { >> if (!memcmp(type_guid->b, hp_devs[i].guid, >> @@ -290,7 +292,32 @@ static void init_vp_index(struct vmbus_channel >> *channel, >> channel->target_vp = 0; >> return; >> } >> - cur_cpu = (++next_vp % max_cpus); >> + >> + /* >> + * Primary channels are distributed evenly across all vcpus we have. >> + * When the host asks us to create subchannels it usually makes us >> + * num_cpus-1 offers and we are supposed to distribute the work >> evenly >> + * among the channel itself and all its subchannels. Make sure they >> are >> + * all assigned to different vcpus. >> + */ >> + if (!primary) >> + cur_cpu = (++next_vp % max_cpus); >> + else { >> + /* >> + * Let's assign the first subchannel of a channel to the >> + * primary->target_cpu+1 and all the subsequent channels >> to >> + * the prev->target_cpu+1. >> + */ >> + spin_lock_irqsave(&primary->lock, flags); >> + if (primary->num_sc == 1) >> + cur_cpu = (primary->target_cpu + 1) % max_cpus; >> + else { >> + prev = list_prev_entry(channel, sc_list); >> + cur_cpu = (prev->target_cpu + 1) % max_cpus; >> + } >> + spin_unlock_irqrestore(&primary->lock, flags); >> + } >> + >> channel->target_cpu = cur_cpu; >> channel->target_vp = hv_context.vp_index[cur_cpu]; >> } >> -- >> 1.9.3 -- Vitaly _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
