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Tue, 21 Jul 2026 05:00:12 +0000 (GMT) Received: from [9.39.17.99] (unknown [9.39.17.99]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 21 Jul 2026 05:00:12 +0000 (GMT) Message-ID: <1dc7d5f2-0e72-4dff-867a-c44156ac3da6@linux.ibm.com> Date: Tue, 21 Jul 2026 10:30:11 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] net/socket: Record preference for synchronous wakeups To: Srikar Dronamraju , LKML , netdev@vger.kernel.org, David S Miller Cc: Ingo Molnar , Peter Zijlstra , Dietmar Eggemann , Dust Li , D Wythe , Eric Dumazet , Jakub Kicinski , Jon Maloy , Kuniyuki Iwashima , linux-sctp@vger.kernel.org, Mahanta Jambigi , Marcelo Ricardo Leitner , Paolo Abeni , Sidraya Jayagond , Simon Horman , Tony Lu , Wen Gu , Wenjia Zhang , Willem de Bruijn , Xin Long , Vincent Guittot , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak References: <20260714013940.4068189-4-srikar@linux.ibm.com> <20260714013940.4068189-5-srikar@linux.ibm.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <20260714013940.4068189-5-srikar@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzIxMDA0NSBTYWx0ZWRfX9y6TVZBkNdYf 1vSY0d1NwBS/tIC6RmeW+LfBuik0x13Ddq8UgA+yVatgwa8iR7dflBgA55XaoOJtlALYkVjPwxk lGPPctIGBgNwQ/hnl5FZemWxlA1vcyFM2eYOqH5SNccX/tTubwdOzUtkFCZGAKzOMpvE//yLxPE 6B1Z1dGOyFG5gbOnPy8KUCjOcvpS0ZlFZKEQrbSyhfXtK+4m4Ty42A5JrqmH7+nRsfQYvd+ATUF nP9qYT7lwVb8A/bsOogioHMv0TImJmttkzl/XbIaMNln5HMF+93DCxrCvu9U6gZkpgRIFSPDm8s N4JaDFvDqYi2WGdfrVipmNzUf83CY2zX8J+nGPPdVvCJ8loG2Gt+5J8cL8ce0KoV67+nRolkrfM 53PnV93j2wX9L2vXWyZPyco4qecCAsol8E0PCgGKEqr6wZB+LkesOUBe4M071Gj/9aye1be/OoM Pb2aJMuAIL9MI9RkUpQ== X-Authority-Analysis: v=2.4 cv=F7ZnsKhN c=1 sm=1 tr=0 ts=6a5efce9 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=kzuGRFPQ2Gws9SZ42BYA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: I-tDB5z4DLULTLxLbb__zXO7lIFkrTi- X-Proofpoint-Spam-Info: AW1haW4tMjYwNzIxMDA0NSBTYWx0ZWRfX/iVf4bxlsPaW 1UzFjEQ3ZsvgeImJQgtYdzZpWwag4MbnPhDDwY4zG0kTnznadt5Pj/yJz/7yZPySDgdjbfmgozM 0HkdBA1MGd1WxRdXFQF8Xkcm+t0MHZU= X-Proofpoint-GUID: lTrg1FdGAGIPkUAcjLqyLUNUU8GOooIl X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-20_06,2026-07-20_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 phishscore=0 bulkscore=0 clxscore=1015 priorityscore=1501 impostorscore=0 lowpriorityscore=0 suspectscore=0 malwarescore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607210045 Hi Srikar. On 7/14/26 7:09 AM, Srikar Dronamraju wrote: > Scheduler differentiates between affine and non-affine wakeups by the > way of sync flags. Scheduler prefers to pull the tasks towards the waker > if the sync flag is set. > > In some cases, socket APIs are blindly requesting sync wakeups. This may > cause load-balance issues and non-optimal performance. > > Record whether the most recent blocking socket operation could benefit > from synchronous wakeups. Subsequent readiness notifications use this > hint to determine whether WF_SYNC should be propagated. > What you mean by recent? Was it info on past set of packets? Could you please explain the flow a bit? Shouldn't it be - if this socket has been defined as nonblock it shouldn't use sync always? > The flag is advisory and affects only wakeup placement decisions. > > Signed-off-by: Srikar Dronamraju > --- > include/net/sock.h | 1 + > net/socket.c | 56 +++++++++++++++++++++++++++++++++++++++------- > 2 files changed, 49 insertions(+), 8 deletions(-) > > diff --git a/include/net/sock.h b/include/net/sock.h > index 51185222aac2..acc6b1976dc4 100644 > --- a/include/net/sock.h > +++ b/include/net/sock.h > @@ -1022,6 +1022,7 @@ enum sock_flags { > SOCK_RCVMARK, /* Receive SO_MARK ancillary data with packet */ > SOCK_RCVPRIORITY, /* Receive SO_PRIORITY ancillary data with packet */ > SOCK_TIMESTAMPING_ANY, /* Copy of sk_tsflags & TSFLAGS_ANY */ > + SOCK_SYNC_WAKEUP, /* Prefer synchronous socket wakeups */ > }; > > #define SK_FLAGS_TIMESTAMP ((1UL << SOCK_TIMESTAMP) | (1UL << SOCK_TIMESTAMPING_RX_SOFTWARE)) > diff --git a/net/socket.c b/net/socket.c > index 63c69a0fa74e..0bcb57ae490e 100644 > --- a/net/socket.c > +++ b/net/socket.c > @@ -1198,15 +1198,27 @@ static void sock_splice_eof(struct file *file) > ops->splice_eof(sock); > } > > +static inline void sock_update_sync_wakeup(struct sock *sk, bool nonblock) > +{ > + if (unlikely(!sk)) > + return; > + > + if (nonblock) { > + if (sock_flag(sk, SOCK_SYNC_WAKEUP)) > + sock_reset_flag(sk, SOCK_SYNC_WAKEUP); > + } else { > + if (!sock_flag(sk, SOCK_SYNC_WAKEUP)) > + sock_set_flag(sk, SOCK_SYNC_WAKEUP); > + } > +} nit: You can combine two if statements. A bit easier to read. static inline void sock_update_sync_wakeup(struct sock *sk, bool nonblock) { if (unlikely(!sk)) return; if (nonblock && sock_flag(sk, SOCK_SYNC_WAKEUP)) sock_reset_flag(sk, SOCK_SYNC_WAKEUP); else if (!nonblock && !sock_flag(sk, SOCK_SYNC_WAKEUP)) sock_set_flag(sk, SOCK_SYNC_WAKEUP); } > + > static ssize_t sock_read_iter(struct kiocb *iocb, struct iov_iter *to) > { > struct file *file = iocb->ki_filp; > struct socket *sock = file->private_data; > struct msghdr msg = {.msg_iter = *to}; > ssize_t res; > - > - if (file->f_flags & O_NONBLOCK || (iocb->ki_flags & IOCB_NOWAIT)) > - msg.msg_flags = MSG_DONTWAIT; > + bool nonblock; > > if (iocb->ki_pos != 0) > return -ESPIPE; > @@ -1214,6 +1226,11 @@ static ssize_t sock_read_iter(struct kiocb *iocb, struct iov_iter *to) > if (!iov_iter_count(to)) /* Match SYS5 behaviour */ > return 0; > > + nonblock = (file->f_flags & O_NONBLOCK) || (iocb->ki_flags & IOCB_NOWAIT); > + if (nonblock) > + msg.msg_flags = MSG_DONTWAIT; > + > + sock_update_sync_wakeup(sock->sk, nonblock); > res = sock_recvmsg(sock, &msg, msg.msg_flags); > *to = msg.msg_iter; > return res; > @@ -1225,13 +1242,17 @@ static ssize_t sock_write_iter(struct kiocb *iocb, struct iov_iter *from) > struct socket *sock = file->private_data; > struct msghdr msg = {.msg_iter = *from}; > ssize_t res; > + bool nonblock; > > if (iocb->ki_pos != 0) > return -ESPIPE; > > - if (file->f_flags & O_NONBLOCK || (iocb->ki_flags & IOCB_NOWAIT)) > + nonblock = (file->f_flags & O_NONBLOCK) || (iocb->ki_flags & IOCB_NOWAIT); > + if (nonblock) > msg.msg_flags = MSG_DONTWAIT; > > + sock_update_sync_wakeup(sock->sk, nonblock); > + > if (sock->type == SOCK_SEQPACKET) > msg.msg_flags |= MSG_EOR; > > @@ -2221,6 +2242,7 @@ int __sys_sendto(int fd, void __user *buff, size_t len, unsigned int flags, > struct sockaddr_storage address; > int err; > struct msghdr msg; > + bool nonblock; > > err = import_ubuf(ITER_SOURCE, buff, len, &msg.msg_iter); > if (unlikely(err)) > @@ -2246,8 +2268,11 @@ int __sys_sendto(int fd, void __user *buff, size_t len, unsigned int flags, > msg.msg_namelen = addr_len; > } > flags &= ~MSG_INTERNAL_SENDMSG_FLAGS; > - if (sock->file->f_flags & O_NONBLOCK) > + nonblock = (sock->file->f_flags & O_NONBLOCK); > + if (nonblock) > flags |= MSG_DONTWAIT; > + > + sock_update_sync_wakeup(sock->sk, nonblock); > msg.msg_flags = flags; > return __sock_sendmsg(sock, &msg); > } > @@ -2284,6 +2309,7 @@ int __sys_recvfrom(int fd, void __user *ubuf, size_t size, unsigned int flags, > }; > struct socket *sock; > int err, err2; > + bool nonblock; > > err = import_ubuf(ITER_DEST, ubuf, size, &msg.msg_iter); > if (unlikely(err)) > @@ -2297,8 +2323,11 @@ int __sys_recvfrom(int fd, void __user *ubuf, size_t size, unsigned int flags, > if (unlikely(!sock)) > return -ENOTSOCK; > > - if (sock->file->f_flags & O_NONBLOCK) > + nonblock = (sock->file->f_flags & O_NONBLOCK); > + if (nonblock) > flags |= MSG_DONTWAIT; > + > + sock_update_sync_wakeup(sock->sk, nonblock); > err = sock_recvmsg(sock, &msg, flags); > > if (err >= 0 && addr != NULL) { > @@ -2634,6 +2663,7 @@ static int ____sys_sendmsg(struct socket *sock, struct msghdr *msg_sys, > unsigned char *ctl_buf = ctl; > int ctl_len; > ssize_t err; > + bool nonblock; > > err = -ENOBUFS; > > @@ -2666,8 +2696,12 @@ static int ____sys_sendmsg(struct socket *sock, struct msghdr *msg_sys, > flags &= ~MSG_INTERNAL_SENDMSG_FLAGS; > msg_sys->msg_flags = flags; > > - if (sock->file->f_flags & O_NONBLOCK) > + nonblock = (sock->file->f_flags & O_NONBLOCK); > + if (nonblock) > msg_sys->msg_flags |= MSG_DONTWAIT; > + > + sock_update_sync_wakeup(sock->sk, nonblock); > + > /* > * If this is sendmmsg() and current destination address is same as > * previously succeeded address, omit asking LSM's decision. > @@ -2887,6 +2921,7 @@ static int ____sys_recvmsg(struct socket *sock, struct msghdr *msg_sys, > unsigned long cmsg_ptr; > int len; > ssize_t err; > + bool nonblock; > > msg_sys->msg_name = &addr; > cmsg_ptr = (unsigned long)msg_sys->msg_control; > @@ -2895,9 +2930,12 @@ static int ____sys_recvmsg(struct socket *sock, struct msghdr *msg_sys, > /* We assume all kernel code knows the size of sockaddr_storage */ > msg_sys->msg_namelen = 0; > > - if (sock->file->f_flags & O_NONBLOCK) > + nonblock = (sock->file->f_flags & O_NONBLOCK); > + if (nonblock) > flags |= MSG_DONTWAIT; > > + sock_update_sync_wakeup(sock->sk, nonblock); > + > if (unlikely(nosec)) > err = sock_recvmsg_nosec(sock, msg_sys, flags); > else > @@ -3056,6 +3094,8 @@ static int do_recvmmsg(int fd, struct mmsghdr __user *mmsg, > if (flags & MSG_WAITFORONE) > flags |= MSG_DONTWAIT; > > + sock_update_sync_wakeup(sock->sk, flags & MSG_WAITFORONE); > + > if (timeout) { > ktime_get_ts64(&timeout64); > *timeout = timespec64_sub(end_time, timeout64);