From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 23C26C43217 for ; Mon, 28 Nov 2022 12:25:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229910AbiK1MZv (ORCPT ); Mon, 28 Nov 2022 07:25:51 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36726 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230388AbiK1MZf (ORCPT ); Mon, 28 Nov 2022 07:25:35 -0500 Received: from out30-130.freemail.mail.aliyun.com (out30-130.freemail.mail.aliyun.com [115.124.30.130]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 91CD91B9FE; Mon, 28 Nov 2022 04:24:08 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045170;MF=tonylu@linux.alibaba.com;NM=1;PH=DS;RN=11;SR=0;TI=SMTPD_---0VVuD7xY_1669638244; Received: from localhost(mailfrom:tonylu@linux.alibaba.com fp:SMTPD_---0VVuD7xY_1669638244) by smtp.aliyun-inc.com; Mon, 28 Nov 2022 20:24:05 +0800 Date: Mon, 28 Nov 2022 20:24:03 +0800 From: Tony Lu To: Wenjia Zhang Cc: Alexandra Winter , Jan Karcher , David Miller , Jakub Kicinski , netdev@vger.kernel.org, linux-s390@vger.kernel.org, Heiko Carstens , Thorsten Winkler , Stefan Raspl , Karsten Graul Subject: Re: [PATCH net] net/smc: Fix expected buffersizes and sync logic Message-ID: Reply-To: Tony Lu References: <40428548-59b9-379c-857c-172db92afc0c@linux.ibm.com> <1a36b6ba-e7bb-6f2a-c460-cf158cb64b1d@linux.ibm.com> <7e0baa06-74e3-e00a-861a-afa8fe1fbdff@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, Nov 28, 2022 at 09:32:45AM +0100, Wenjia Zhang wrote: > > > On 28.11.22 05:33, Tony Lu wrote: > > On Fri, Nov 25, 2022 at 11:59:46AM +0100, Alexandra Winter wrote: > > > > > > > > > On 25.11.22 08:05, Tony Lu wrote: > > > > On Fri, Nov 25, 2022 at 07:15:33AM +0100, Jan Karcher wrote: > > > > > > > > > > > > > > > On 24/11/2022 15:07, Alexandra Winter wrote: > > > > > > > > > > > > > > > > > > On 24.11.22 14:00, Alexandra Winter wrote: > > > > > > > > > > > > > > > > > > > [ ... ]>>>>> On Wed, Nov 23, 2022 at 11:49:07AM +0100, Jan Karcher wrote: > > > > > > > > > > > The fixed commit changed the expected behavior of buffersizes > > > > > > > > > > > set by the user using the setsockopt mechanism. > > > > > > > > > > > Before the fixed patch the logic for determining the buffersizes used > > > > > > > > > > > was the following: > > > > > > > > > > > > > > > > > > > > > > default = net.ipv4.tcp_{w|r}mem[1] > > > > > > Jan, you explained to me: "the minima is 16Kib. This is enforced in smc_compress_bufsize > > > > > > which would move any value <= 16Kib into bucket 0 - which is 16KiB " > > > > > > net.ipv4.tcp_wmem[1] defaults to 8Kib. So in the default case (unchanged net.ipv4.tcp_wmem[1]) > > > > > > the default for the send path is not net.ipv4.tcp_wmem[1]. Should be clarified here. > > > > > > > > > > The default value is still set to the net.ipv4.tcp_{w|r}mem[1]. This is a > > > > > *very* top level overview about what is happening and *not* a documentation. > > > > > I don't really want to explain the full code flow here. > > > > > > > > > > What we still should do - as Tony aggreed on - is documenting the SMC > > > > > behavior. This is a follow up on my list. > > > > > > > > Hello Jan and Alexandra, > > > > > > > > It looks like the misalignment of information is causing some trouble, > > > > which is introduced by my patch. Maybe we could have an off-maillist and > > > > online meeting to discussion? > > > > > > > > We have some progress updates of scalability, and we are really like the > > > > extension of SMC-D. Also we have some ideas for SMC, in case of > > > > misalignment of information, we'd like to put them on the table and > > > > discuss them earlier. Maybe an online meeting is an efficient way. What > > > > do you think? > > > > > > > > If possible, I would prepared the meetings and topics and send them to > > > > everyone first. > > > > > > > > Cheers, > > > > Tony Lu > > > > > > > > > > Thanks a lot for your constructive proposals Tony. Yes, we should have a discussion off-mailinglist > > > about future topics. > > > > I will prepare the discussion off-maillinglist ASAP. The email will be > > sent out when it's ready. And Jan, What about your opinion? > > > > Cheers, > > Tony Lu > > > Hi Tony, > > Sorry for the flurry we brought! > > It's very nice to know that you got progress on the scalability. > > Firstly the off-millinglist is a good idea! Let's know if yor're ready. > > About the meetings I would ask for your understanding that I still can not > give any guarantee. But I would let you know ASAP after I talk to our team. Sure, looking forward to your reply. Cheers, Tony Lu > > Best, > Wenjia > > > > > > My remaining concern for this fix is the default values (user does not use setsockopt, nor > > > changes the new sysfs parameters, nor changes tcp defaults): > > > > > > > before 0227f058aa29 ("net/smc: Unbind r/w buffer size from clcsock and make them tunable") > > > send: 16k recv: 64k > > > > > > > after net/smc: Fix expected buffersizes and sync logic (this patch) > > > > > > > send: 16k recv: 128k > > > > > > @Jan, as this is the only patch you want to send to net, please change the default size of > > > the receive buffers back to 64k (I don't care how). > > > > > > > > > > > > > > > > > > > > > > sockopt = the setsockopt mechanism > > > > > > > > > > > val = the value assigned in default or via setsockopt > > > > > > > > > > > sk_buf = short for sk_{snd|rcv}buf > > > > > > > > > > > real_buf = the real size of the buffer (sk_buf_size in __smc_buf_create) > > > > > > > > > > > > > > > > > > > > > > exposed | net/core/sock.c | af_smc.c | smc_core.c > > > > > > > > > > > | | | > > > > > > > > > > > +---------+ | | +------------+ | +-------------------+ > > > > > > > > > > > | default |----------------------| sk_buf=val |---| real_buf=sk_buf/2 | > > > > > > > > > > > +---------+ | | +------------+ | +-------------------+ > > > > > > > > > > > | | | ^ > > > > > > > > > > > | | | | > > > > > > > > > > > +---------+ | +--------------+ | | | > > > > > > > > > > > | sockopt |---| sk_buf=val*2 |-----------------------| > > > > > > > > > > > +---------+ | +--------------+ | | > > > > > > > > > > > | | | > > > > > > > > > > > > > > > > > > > > > > The fixed patch introduced a dedicated sysctl for smc > > > > > > > > > > > and removed the /2 in smc_core.c resulting in the following flow: > > > > > > > > > > > > > > > > > > > > > > default = net.smc.{w|r}mem (which defaults to net.ipv4.tcp_{w|r}mem[1]) > > > > > > > > > > > sockopt = the setsockopt mechanism > > > > > > > > > > > val = the value assigned in default or via setsockopt > > > > > > > > > > > sk_buf = short for sk_{snd|rcv}buf > > > > > > > > > > > real_buf = the real size of the buffer (sk_buf_size in __smc_buf_create) > > > > > > > > > > > > > > > > > > > > > > exposed | net/core/sock.c | af_smc.c | smc_core.c > > > > > > > > > > > | | | > > > > > > > > > > > +---------+ | | +------------+ | +-----------------+ > > > > > > > > > > > | default |----------------------| sk_buf=val |---| real_buf=sk_buf | > > > > > > > > > > > +---------+ | | +------------+ | +-----------------+ > > > > > > > > > > > | | | ^ > > > > > > > > > > > | | | | > > > > > > > > > > > +---------+ | +--------------+ | | | > > > > > > > > > > > | sockopt |---| sk_buf=val*2 |-----------------------| > > > > > > > > > > > +---------+ | +--------------+ | | > > > > > > > > > > > | | | > > > > > > > > > > > > > > > > > > > > > > This would result in double of memory used for existing configurations > > > > > > > > > > > that are using setsockopt. > > > > > > > > > > > > > > > > > > > > Firstly, thanks for your detailed diagrams :-) > > > > > > > > > > > > > > > > > > > > And the original decision to use user-provided values rather than > > > > > > > > > > value/2 to follow the instructions of the socket manual [1]. > > > > > > > > > > > > > > > > > > > > SO_RCVBUF > > > > > > > > > > Sets or gets the maximum socket receive buffer in bytes. > > > > > > > > > > The kernel doubles this value (to allow space for > > > > > > > > > > bookkeeping overhead) when it is set using setsockopt(2), > > > > > > > > > > and this doubled value is returned by getsockopt(2). The > > > > > > > > > > default value is set by the > > > > > > > > > > /proc/sys/net/core/rmem_default file, and the maximum > > > > > > > > > > allowed value is set by the /proc/sys/net/core/rmem_max > > > > > > > > > > file. The minimum (doubled) value for this option is 256. > > > > > > > > > > > > > > > > > > > > [1] https://man7.org/linux/man-pages/man7/socket.7.html > > > > > > > > > > > > > > > > > > > > The user of SMC should know that setsockopt() with SO_{RCV|SND}BUF will > > > > > > > > > > > > > > > > > > I totally agree that an educated user of SMC should know about that behavior > > > > > > > > > if they decide to use it. > > > > > > > > > We do provide our users preload libraries where they can pass preferred > > > > > > > > > buffersizes via arguments and we handle the Sockopts for them. > > > > > > > > > > > > > > > > > > > double the values in kernel, and getsockopt() will return the doubled > > > > > > > > > > values. So that they should use half of the values which are passed to > > > > > > > > > > setsockopt(). The original patch tries to make things easier in SMC and > > > > > > > > > > let user-space to handle them following the socket manual. > > > > > > > > > > > > > > > > > > > > > SMC historically decided to use the explicit value given by the user > > > > > > > > > > > to allocate the memory. This is why we used the /2 in smc_core.c. > > > > > > > > > > > That logic was not applied to the default value. > > > > > > > > > > > > > > > > > > > > Yep, let back to the patch which introduced smc_{w|r}mem knobs, it's a > > > > > > > > > > trade-off to follow original logic of SMC, or follow the socket manual. > > > > > > > > > > We decides to follow the instruction of manuals in the end. > > > > > > > > > > > > > > > > > > I understand the point. I spend a lot of time trying to decide what to do. > > > > > > > > > > > > > > > > > > Since it was an intentional decision to not follow the general socket > > > > > > > > > option, and we do not have anyone complaining we do not really have a reason > > > > > > > > > to change it. > > > > > > > > > Changing it means that users with existing configurations would have to > > > > > > > > > change their configs on an update or suddenly expect double the memory > > > > > > > > > consumption. > > > > > > > > > That's why we in the end preffered to stay with the current logic. > > > > > > > > > > > > > > > > I can't agree with you more with the points to follow the historic logic > > > > > > > > and not break the user-space applications. > > > > > > > > > > > > > > > > > I'm thinking that maybe - if we stay with the historic logic - we should > > > > > > > > > document that desicion somewhere. So that in the future, if a user that > > > > > > > > > expects the man page behavior, has a way to understand what SMC is doing. > > > > > > > > > What do oyu think? > > > > > > > > > > > > > > > > Yep, we _really_ need to document it if we change the convention. > > > > > > > > Actually, I spent a lot of time to find the history about the logic of > > > > > > > > buffer (/2 and *2) in SMC. So I'm really in favor of adding > > > > > > > > documentation, at least code comments to help others to understand them. > > > > > > > > > > > > > > > > Cheers, > > > > > > > > Tony Lu > > > > > > > Iiuc you are changing the default values in this a patch and your other patch: > > > > > > > Default values for real_buf for send and receive: > > > > > > > > > > > > > > before 0227f058aa29 ("net/smc: Unbind r/w buffer size from clcsock and make them tunable") > > > > > > > real_buf=net.ipv4.tcp_{w|r}mem[1]/2 send: 8k recv: 64k > > > > > > see above: send: 16k recv: 64k > > > > > > > after 0227f058aa29 ("net/smc: Unbind r/w buffer size from clcsock and make them tunable") > > > > > > > real_buf=net.ipv4.tcp_{w|r}mem[1] send: 16k (16*1024) recv: 128k (131072) > > > > > > > > > > > > > > after net/smc: Fix expected buffersizes and sync logic > > > > > > > real_buf=net.ipv4.tcp_{w|r}mem[1] send: 16k (16*1024) recv: 128k (131072) > > > > > > > > > > > > > > after net/smc: Unbind smc control from tcp control > > > > > > > real_buf=SMC_*BUF_INIT_SIZE send: 16k (16384) recv: 64k (65536) > > > > > > > > > > > > > > If my understanding is correct, then I nack this. > > > > > > > Defaults should be restored to the values before 0227f058aa29. > > > > > > > Otherwise users will notice a change in memory usage that needs to > > > > > > > be avoided or announced more explicitely. (and don't change them twice) > > > > > > See above, I stand corrected. However this patch fixes/restores the buffersize > > > > > > for setsockopt, but not for the default recieve path. > > > > > > Could you please clarify that in the title and description? > > > > > > > > > > > > > > > > I am trying to keep the commit title as crisp as possible while providing > > > > > enough information and set the context in the commit message: > > > > > > > > > > "The fixed commit changed the expected behavior of buffersizes set by the > > > > > user using the setsockopt mechanism." > > > > > > > > > > + There is now a whole e-mail thread to consult in case of any further > > > > > questions. > > > > > > > > > > Thank you for your comments > > > > > - Jan > > > > > > > > > > > Reviewed-by: Alexandra Winter > > > > > > > > > - Jan > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Cheers, > > > > > > > > > > Tony Lu > > > > > > > > > > > > > > > > > > > > > Since we now have our own sysctl, which is also exposed to the user, > > > > > > > > > > > we should sync the logic in a way that both values are the real value > > > > > > > > > > > used by our code and shown by smc_stats. To achieve this this patch > > > > > > > > > > > changes the behavior to: > > > > > > > > > > > > > > > > > > > > > > default = net.smc.{w|r}mem (which defaults to net.ipv4.tcp_{w|r}mem[1]) > > > > > > > > > > > sockopt = the setsockopt mechanism > > > > > > > > > > > val = the value assigned in default or via setsockopt > > > > > > > > > > > sk_buf = short for sk_{snd|rcv}buf > > > > > > > > > > > real_buf = the real size of the buffer (sk_buf_size in __smc_buf_create) > > > > > > > > > > > > > > > > > > > > > > exposed | net/core/sock.c | af_smc.c | smc_core.c > > > > > > > > > > > | | | > > > > > > > > > > > +---------+ | | +-------------+ | +-----------------+ > > > > > > > > > > > | default |----------------------| sk_buf=val*2|---|real_buf=sk_buf/2| > > > > > > > > > > > +---------+ | | +-------------+ | +-----------------+ > > > > > > > > > > > | | | ^ > > > > > > > > > > > | | | | > > > > > > > > > > > +---------+ | +--------------+ | | | > > > > > > > > > > > | sockopt |---| sk_buf=val*2 |------------------------| > > > > > > > > > > > +---------+ | +--------------+ | | > > > > > > > > > > > | | | > > > > > > > > > > > > > > > > > > > > > > This way both paths follow the same pattern and the expected behavior > > > > > > > > > > > is re-established. > > > > > > > > > > > > > > > > > > > > > > Fixes: 0227f058aa29 ("net/smc: Unbind r/w buffer size from clcsock and make them tunable") > > > > > > > > > > > Signed-off-by: Jan Karcher > > > > > > > > > > > Reviewed-by: Wenjia Zhang > > > > > > > > > > > --- > > > > > > > > > > > net/smc/af_smc.c | 9 +++++++-- > > > > > > > > > > > net/smc/smc_core.c | 8 ++++---- > > > > > > > > > > > 2 files changed, 11 insertions(+), 6 deletions(-) > > > > > > > > > > > > > > > > > > > > > > diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c > > > > > > > > > > > index 036532cf39aa..a8c84e7bac99 100644 > > > > > > > > > > > --- a/net/smc/af_smc.c > > > > > > > > > > > +++ b/net/smc/af_smc.c > > > > > > > > > > > @@ -366,6 +366,7 @@ static void smc_destruct(struct sock *sk) > > > > > > > > > > > static struct sock *smc_sock_alloc(struct net *net, struct socket *sock, > > > > > > > > > > > int protocol) > > > > > > > > > > > { > > > > > > > > > > > + int buffersize_without_overhead; > > > > > > > > > > > struct smc_sock *smc; > > > > > > > > > > > struct proto *prot; > > > > > > > > > > > struct sock *sk; > > > > > > > > > > > @@ -379,8 +380,12 @@ static struct sock *smc_sock_alloc(struct net *net, struct socket *sock, > > > > > > > > > > > sk->sk_state = SMC_INIT; > > > > > > > > > > > sk->sk_destruct = smc_destruct; > > > > > > > > > > > sk->sk_protocol = protocol; > > > > > > > > > > > - WRITE_ONCE(sk->sk_sndbuf, READ_ONCE(net->smc.sysctl_wmem)); > > > > > > > > > > > - WRITE_ONCE(sk->sk_rcvbuf, READ_ONCE(net->smc.sysctl_rmem)); > > > > > > > > > > > + buffersize_without_overhead = > > > > > > > > > > > + min_t(int, READ_ONCE(net->smc.sysctl_wmem), INT_MAX / 2); > > > > > > > > > > > + WRITE_ONCE(sk->sk_sndbuf, buffersize_without_overhead * 2); > > > > > > > > > > > + buffersize_without_overhead = > > > > > > > > > > > + min_t(int, READ_ONCE(net->smc.sysctl_rmem), INT_MAX / 2); > > > > > > > > > > > + WRITE_ONCE(sk->sk_rcvbuf, buffersize_without_overhead * 2); > > > > > > > > > > > smc = smc_sk(sk); > > > > > > > > > > > INIT_WORK(&smc->tcp_listen_work, smc_tcp_listen_work); > > > > > > > > > > > INIT_WORK(&smc->connect_work, smc_connect_work); > > > > > > > > > > > diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c > > > > > > > > > > > index 00fb352c2765..36850a2ae167 100644 > > > > > > > > > > > --- a/net/smc/smc_core.c > > > > > > > > > > > +++ b/net/smc/smc_core.c > > > > > > > > > > > @@ -2314,10 +2314,10 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb) > > > > > > > > > > > if (is_rmb) > > > > > > > > > > > /* use socket recv buffer size (w/o overhead) as start value */ > > > > > > > > > > > - sk_buf_size = smc->sk.sk_rcvbuf; > > > > > > > > > > > + sk_buf_size = smc->sk.sk_rcvbuf / 2; > > > > > > > > > > > else > > > > > > > > > > > /* use socket send buffer size (w/o overhead) as start value */ > > > > > > > > > > > - sk_buf_size = smc->sk.sk_sndbuf; > > > > > > > > > > > + sk_buf_size = smc->sk.sk_sndbuf / 2; > > > > > > > > > > > for (bufsize_short = smc_compress_bufsize(sk_buf_size, is_smcd, is_rmb); > > > > > > > > > > > bufsize_short >= 0; bufsize_short--) { > > > > > > > > > > > @@ -2376,7 +2376,7 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb) > > > > > > > > > > > if (is_rmb) { > > > > > > > > > > > conn->rmb_desc = buf_desc; > > > > > > > > > > > conn->rmbe_size_short = bufsize_short; > > > > > > > > > > > - smc->sk.sk_rcvbuf = bufsize; > > > > > > > > > > > + smc->sk.sk_rcvbuf = bufsize * 2; > > > > > > > > > > > atomic_set(&conn->bytes_to_rcv, 0); > > > > > > > > > > > conn->rmbe_update_limit = > > > > > > > > > > > smc_rmb_wnd_update_limit(buf_desc->len); > > > > > > > > > > > @@ -2384,7 +2384,7 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb) > > > > > > > > > > > smc_ism_set_conn(conn); /* map RMB/smcd_dev to conn */ > > > > > > > > > > > } else { > > > > > > > > > > > conn->sndbuf_desc = buf_desc; > > > > > > > > > > > - smc->sk.sk_sndbuf = bufsize; > > > > > > > > > > > + smc->sk.sk_sndbuf = bufsize * 2; > > > > > > > > > > > atomic_set(&conn->sndbuf_space, bufsize); > > > > > > > > > > > } > > > > > > > > > > > return 0; > > > > > > > > > > > -- > > > > > > > > > > > 2.34.1