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Message-ID: <20230526064531.zohcgjbaraq7c2ui@soft-dev3-1> Date: Fri, 26 May 2023 08:45:31 +0200 From: Horatiu Vultur <horatiu.vultur@...rochip.com> To: Haiyang Zhang <haiyangz@...rosoft.com> CC: "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, Dexuan Cui <decui@...rosoft.com>, KY Srinivasan <kys@...rosoft.com>, Paul Rosswurm <paulros@...rosoft.com>, "olaf@...fle.de" <olaf@...fle.de>, "vkuznets@...hat.com" <vkuznets@...hat.com>, "davem@...emloft.net" <davem@...emloft.net>, "wei.liu@...nel.org" <wei.liu@...nel.org>, "edumazet@...gle.com" <edumazet@...gle.com>, "kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>, "leon@...nel.org" <leon@...nel.org>, Long Li <longli@...rosoft.com>, "ssengar@...ux.microsoft.com" <ssengar@...ux.microsoft.com>, "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>, "daniel@...earbox.net" <daniel@...earbox.net>, "john.fastabend@...il.com" <john.fastabend@...il.com>, "bpf@...r.kernel.org" <bpf@...r.kernel.org>, "ast@...nel.org" <ast@...nel.org>, Ajay Sharma <sharmaajay@...rosoft.com>, "hawk@...nel.org" <hawk@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "stable@...r.kernel.org" <stable@...r.kernel.org> Subject: Re: [PATCH net] net: mana: Fix perf regression: remove rx_cqes, tx_cqes counters The 05/25/2023 14:34, Haiyang Zhang wrote: > > > -----Original Message----- > > From: Horatiu Vultur <horatiu.vultur@...rochip.com> > > Sent: Thursday, May 25, 2023 2:49 AM > > To: Haiyang Zhang <haiyangz@...rosoft.com> > > Cc: linux-hyperv@...r.kernel.org; netdev@...r.kernel.org; Dexuan Cui > > <decui@...rosoft.com>; KY Srinivasan <kys@...rosoft.com>; Paul Rosswurm > > <paulros@...rosoft.com>; olaf@...fle.de; vkuznets@...hat.com; > > davem@...emloft.net; wei.liu@...nel.org; edumazet@...gle.com; > > kuba@...nel.org; pabeni@...hat.com; leon@...nel.org; Long Li > > <longli@...rosoft.com>; ssengar@...ux.microsoft.com; linux- > > rdma@...r.kernel.org; daniel@...earbox.net; john.fastabend@...il.com; > > bpf@...r.kernel.org; ast@...nel.org; Ajay Sharma > > <sharmaajay@...rosoft.com>; hawk@...nel.org; linux- > > kernel@...r.kernel.org; stable@...r.kernel.org > > Subject: Re: [PATCH net] net: mana: Fix perf regression: remove rx_cqes, > > tx_cqes counters > > > > [Some people who received this message don't often get email from > > horatiu.vultur@...rochip.com. Learn why this is important at > > https://aka.ms/LearnAboutSenderIdentification ] > > > > The 05/24/2023 14:22, Haiyang Zhang wrote: > > > > Hi Haiyang, > > > > > > > > The apc->eth_stats.rx_cqes is one per NIC (vport), and it's on the > > > frequent and parallel code path of all queues. So, r/w into this > > > single shared variable by many threads on different CPUs creates a > > > lot caching and memory overhead, hence perf regression. And, it's > > > not accurate due to the high volume concurrent r/w. > > > > Do you have any numbers to show the improvement of this change? > > The numbers are not published. The perf regression of the previous > patch is very significant, and this patch eliminates the regression. > > > > > > > > > Since the error path of mana_poll_rx_cq() already has warnings, so > > > keeping the counter and convert it to a per-queue variable is not > > > necessary. So, just remove this counter from this high frequency > > > code path. > > > > > > Also, remove the tx_cqes counter for the same reason. We have > > > warnings & other counters for errors on that path, and don't need > > > to count every normal cqe processing. > > > > Will you not have problems with the counter 'apc->eth_stats.tx_cqe_err'? > > It is not in the hot path but you will have concurrent access to it. > > Yes, but that error happens rarely, so a shared variable is good enough. So, I > don't change it in this patch. OK, I understand. Maybe this can be fixed in a different patch at a later point. Thanks. Reviwed-by: Horatiu Vultur <horatiu.vultur@...rochip.com> > > Thanks, > - Haiyang > -- /Horatiu
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