On Wed, 22 Mar 2017 23:40:04 +0000 Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: > On Wed, Mar 22, 2017 at 07:39:17PM +0200, Tariq Toukan wrote: > > > > > This modification may slow allocations from IRQ context slightly > > > > > but the > > > > > main gain from the per-cpu allocator is that it scales better for > > > > > allocations from multiple contexts. There is an implicit > > > > > assumption that > > > > > intensive allocations from IRQ contexts on multiple CPUs from a single > > > > > NUMA node are rare > > Hi Mel, Jesper, and all. > > > > This assumption contradicts regular multi-stream traffic that is naturally > > handled > > over close numa cores. I compared iperf TCP multistream (8 streams) > > over CX4 (mlx5 driver) with kernels v4.10 (before this series) vs > > kernel v4.11-rc1 (with this series). > > I disabled the page-cache (recycle) mechanism to stress the page allocator, > > and see a drastic degradation in BW, from 47.5 G in v4.10 to 31.4 G in > > v4.11-rc1 (34% drop). > > I noticed queued_spin_lock_slowpath occupies 62.87% of CPU time. > > Can you get the stack trace for the spin lock slowpath to confirm it's > from IRQ context? AFAIK allocations happen in softirq. Argh and during review I missed that in_interrupt() also covers softirq. To Mel, can we use a in_irq() check instead? (p.s. just landed and got home) -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
