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RE: [Xen-devel][Pv-ops][PATCH 0/4 v4] Netback multiple threads support


Do you have comments on this version of patch?


Xu, Dongxiao wrote:
> This is netback multithread support patchset version 4.
> Main Changes from v3:
> 1. Patchset is against xen/next tree.
> 2. Merge group and idx into netif->mapping.
> 3. Use vmalloc to allocate netbk structures.
> Main Changes from v2:
> 1. Merge "group" and "idx" into "netif->mapping", therefore
> page_ext is not used now.
> 2. Put netbk_add_netif() and netbk_remove_netif() into
> __netif_up() and __netif_down().
> 3. Change the usage of kthread_should_stop().
> 4. Use __get_free_pages() to replace kzalloc().
> 5. Modify the changes to netif_be_dbg().
> 6. Use MODPARM_netback_kthread to determine whether using
> tasklet or kernel thread.
> 7. Put small fields in the front, and large arrays in the end of
> struct xen_netbk.
> 8. Add more checks in netif_page_release().
> Current netback uses one pair of tasklets for Tx/Rx data transaction.
> Netback tasklet could only run at one CPU at a time, and it is used to
> serve all the netfronts. Therefore it has become a performance bottle
> neck. This patch is to use multiple tasklet pairs to replace the
> current single pair in dom0.
> Assuming that Dom0 has CPUNR VCPUs, we define CPUNR kinds of
> tasklets pair (CPUNR for Tx, and CPUNR for Rx). Each pare of tasklets
> serve specific group of netfronts. Also for those global and static
> variables, we duplicated them for each group in order to avoid the
> spinlock.
> PATCH 01: Generilize static/global variables into 'struct xen_netbk'.
> PATCH 02: Introduce a new struct type page_ext.
> PATCH 03: Multiple tasklets support.
> PATCH 04: Use Kernel thread to replace the tasklet.
> Recently I re-tested the patchset with Intel 10G multi-queue NIC
> device, and use 10 outside 1G NICs to do netperf tests with that 10G
> NIC. 
> Case 1: Dom0 has more than 10 vcpus pinned with each physical CPU.
> With the patchset, the performance is 2x of the original throughput.
> Case 2: Dom0 has 4 vcpus pinned with 4 physical CPUs.
> With the patchset, the performance is 3.7x of the original throughput.
> when we test this patch, we found that the domain_lock in grant table
> operation (gnttab_copy()) becomes a bottle neck. We temporarily
> remove the global domain_lock to achieve good performance.

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