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Date: Tue, 4 Feb 2014 00:04:07 +0530 From: Mugunthan V N <mugunthanvnm@...com> To: Florian Fainelli <f.fainelli@...il.com> CC: Ben Hutchings <bhutchings@...arflare.com>, netdev <netdev@...r.kernel.org> Subject: Re: TI CPSW Ethernet Tx performance regression Hi On Friday 17 January 2014 05:05 AM, Florian Fainelli wrote: > Whenever I had bad TX performance with hardware, the culprit was that > transmit buffers were not freed quickly enough so the transmit > scheduler cannot push as many packets as expected. When this happens, > the root cause for me was bad TX interrupt which messed up the TX flow > control, but there are plenty other stuff that can go wrong. > > You could try to check a few things like TX interrupt rate for the > same workload on both kernels, dump the queue usage every few seconds > etc... I did a further analysis using oprofile and found some more info. In v3.2 kernel most of the time is spend in csum_partial_copy_from_user and cpdma_chan_submit which are in the path of tx but the dump in v3.12 cpu is held more in __do_softirq and __irq_put_desc_unlock. I think because of this Tx performance is affected. Since __do_softirq is used to invode NAPI, how to reduce its priority or is there any other code that I should be looking into? Pasting the O-Profile dump with iperf running in v3.2 and v3.12 kernel v3.2: ==== samples % app name symbol name 33152 9.3792 vmlinux-3.2 csum_partial_copy_from_user 23960 6.7786 vmlinux-3.2 cpdma_chan_submit 19288 5.4569 vmlinux-3.2 __do_softirq 13425 3.7981 vmlinux-3.2 __irq_put_desc_unlock 11065 3.1305 vmlinux-3.2 tcp_packet 8458 2.3929 vmlinux-3.2 __cpdma_chan_free 8386 2.3725 vmlinux-3.2 cpdma_ctlr_int_ctrl 7316 2.0698 vmlinux-3.2 __cpdma_chan_process 5186 1.4672 vmlinux-3.2 tcp_transmit_skb 5118 1.4480 vmlinux-3.2 ipt_do_table 4954 1.4016 vmlinux-3.2 kfree 4857 1.3741 vmlinux-3.2 nf_iterate 4797 1.3571 vmlinux-3.2 tcp_ack 4511 1.2762 vmlinux-3.2 __kmalloc 4433 1.2542 vmlinux-3.2 v7_dma_inv_range 4393 1.2428 vmlinux-3.2 nf_conntrack_in 4069 1.1512 vmlinux-3.2 tcp_sendmsg 3607 1.0205 vmlinux-3.2 local_bh_enable 3148 0.8906 vmlinux-3.2 __memzero 3127 0.8847 vmlinux-3.2 csum_partial 2850 0.8063 vmlinux-3.2 __alloc_skb 2825 0.7992 vmlinux-3.2 ip_queue_xmit 2559 0.7240 vmlinux-3.2 tcp_write_xmit 2399 0.6787 vmlinux-3.2 clocksource_read_cycles 2091 0.5916 vmlinux-3.2 dev_hard_start_xmit v3.12: ===== samples % app name symbol name 9040 15.8034 vmlinux __do_softirq 6410 11.2057 vmlinux __irq_put_desc_unlock 3584 6.2654 vmlinux cpdma_chan_submit 3250 5.6815 vmlinux csum_partial_copy_from_user 3070 5.3669 vmlinux __cpdma_chan_process 2894 5.0592 vmlinux resend_irqs 2567 4.4875 vmlinux cpdma_ctlr_int_ctrl 2214 3.8704 vmlinux mod_timer 1922 3.3600 vmlinux lock_acquire 1402 2.4509 vmlinux __cpdma_chan_free 1063 1.8583 vmlinux local_bh_enable 783 1.3688 vmlinux cpdma_check_free_tx_desc 668 1.1678 vmlinux lock_is_held 610 1.0664 vmlinux __kmalloc_track_caller 584 1.0209 vmlinux lock_release 559 0.9772 vmlinux kmem_cache_alloc 557 0.9737 vmlinux kfree 460 0.8042 vmlinux tcp_transmit_skb 429 0.7500 vmlinux tcp_ack 418 0.7307 vmlinux tcp_sendmsg 378 0.6608 vmlinux kmem_cache_free 366 0.6398 vmlinux ip_queue_xmit 363 0.6346 vmlinux cache_alloc_refill 351 0.6136 vmlinux sub_preempt_count 347 0.6066 vmlinux napi_complete 335 0.5856 vmlinux __alloc_skb 311 0.5437 vmlinux ip_finish_output -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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