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Message-ID: <e07e0ad8-32da-452e-809a-f3dfeb8b56f3@gmail.com>
Date: Sat, 10 May 2025 16:18:59 +0900
From: Daisuke Matsuda <dskmtsd@...il.com>
To: Zhu Yanjun <yanjun.zhu@...ux.dev>, linux-kernel@...r.kernel.org,
linux-rdma@...r.kernel.org, leon@...nel.org, jgg@...pe.ca,
zyjzyj2000@...il.com
Subject: Re: [PATCH for-next v2 1/2] RDMA/rxe: Implement synchronous prefetch
for ODP MRs
On 2025/05/10 13:43, Zhu Yanjun wrote:
>
> 在 2025/5/10 4:46, Daisuke Matsuda 写道:
>> On 2025/05/10 0:19, Zhu Yanjun wrote:
>>> On 03.05.25 15:42, Daisuke Matsuda wrote:
>>>> Minimal implementation of ibv_advise_mr(3) requires synchronous calls being
>>>> successful with the IBV_ADVISE_MR_FLAG_FLUSH flag. Asynchronous requests,
>>>> which are best-effort, will be added subsequently.
>>>>
>>>> Signed-off-by: Daisuke Matsuda <dskmtsd@...il.com>
>>>> ---
>>>> drivers/infiniband/sw/rxe/rxe.c | 7 +++
>>>> drivers/infiniband/sw/rxe/rxe_loc.h | 10 ++++
>>>> drivers/infiniband/sw/rxe/rxe_odp.c | 86 +++++++++++++++++++++++++++++
>>>> 3 files changed, 103 insertions(+)
>>>>
>>>> diff --git a/drivers/infiniband/sw/rxe/rxe.c b/drivers/infiniband/sw/rxe/rxe.c
>>>> index 3a77d6db1720..e891199cbdef 100644
>>>> --- a/drivers/infiniband/sw/rxe/rxe.c
>>>> +++ b/drivers/infiniband/sw/rxe/rxe.c
>>>> @@ -34,6 +34,10 @@ void rxe_dealloc(struct ib_device *ib_dev)
>>>> mutex_destroy(&rxe->usdev_lock);
>>>> }
>>>> +static const struct ib_device_ops rxe_ib_dev_odp_ops = {
>>>> + .advise_mr = rxe_ib_advise_mr,
>>>> +};
>>>> +
>>>> /* initialize rxe device parameters */
>>>> static void rxe_init_device_param(struct rxe_dev *rxe, struct net_device *ndev)
>>>> {
>>>> @@ -103,6 +107,9 @@ static void rxe_init_device_param(struct rxe_dev *rxe, struct net_device *ndev)
>>>> rxe->attr.odp_caps.per_transport_caps.rc_odp_caps |= IB_ODP_SUPPORT_SRQ_RECV;
>>>> rxe->attr.odp_caps.per_transport_caps.rc_odp_caps |= IB_ODP_SUPPORT_FLUSH;
>>>> rxe->attr.odp_caps.per_transport_caps.rc_odp_caps |= IB_ODP_SUPPORT_ATOMIC_WRITE;
>>>> +
>>>> + /* set handler for ODP prefetching API - ibv_advise_mr(3) */
>>>> + ib_set_device_ops(&rxe->ib_dev, &rxe_ib_dev_odp_ops);
>>>> }
>>>> }
>>>> diff --git a/drivers/infiniband/sw/rxe/rxe_loc.h b/drivers/infiniband/sw/rxe/rxe_loc.h
>>>> index f7dbb9cddd12..21b070f3dbb8 100644
>>>> --- a/drivers/infiniband/sw/rxe/rxe_loc.h
>>>> +++ b/drivers/infiniband/sw/rxe/rxe_loc.h
>>>> @@ -197,6 +197,9 @@ enum resp_states rxe_odp_atomic_op(struct rxe_mr *mr, u64 iova, int opcode,
>>>> int rxe_odp_flush_pmem_iova(struct rxe_mr *mr, u64 iova,
>>>> unsigned int length);
>>>> enum resp_states rxe_odp_do_atomic_write(struct rxe_mr *mr, u64 iova, u64 value);
>>>> +int rxe_ib_advise_mr(struct ib_pd *pd, enum ib_uverbs_advise_mr_advice advice,
>>>> + u32 flags, struct ib_sge *sg_list, u32 num_sge,
>>>> + struct uverbs_attr_bundle *attrs);
>>>> #else /* CONFIG_INFINIBAND_ON_DEMAND_PAGING */
>>>> static inline int
>>>> rxe_odp_mr_init_user(struct rxe_dev *rxe, u64 start, u64 length, u64 iova,
>>>> @@ -225,6 +228,13 @@ static inline enum resp_states rxe_odp_do_atomic_write(struct rxe_mr *mr,
>>>> {
>>>> return RESPST_ERR_UNSUPPORTED_OPCODE;
>>>> }
>>>> +static inline int rxe_ib_advise_mr(struct ib_pd *pd, enum ib_uverbs_advise_mr_advice advice,
>>>> + u32 flags, struct ib_sge *sg_list, u32 num_sge,
>>>> + struct uverbs_attr_bundle *attrs)
>>>> +{
>>>> + return -EOPNOTSUPP;
>>>> +}
>>>> +
>>>> #endif /* CONFIG_INFINIBAND_ON_DEMAND_PAGING */
>>>> #endif /* RXE_LOC_H */
>>>> diff --git a/drivers/infiniband/sw/rxe/rxe_odp.c b/drivers/infiniband/sw/rxe/rxe_odp.c
>>>> index 6149d9ffe7f7..e5c60b061d7e 100644
>>>> --- a/drivers/infiniband/sw/rxe/rxe_odp.c
>>>> +++ b/drivers/infiniband/sw/rxe/rxe_odp.c
>>>> @@ -424,3 +424,89 @@ enum resp_states rxe_odp_do_atomic_write(struct rxe_mr *mr, u64 iova, u64 value)
>>>> return RESPST_NONE;
>>>> }
>>>> +
>>>> +static int rxe_ib_prefetch_sg_list(struct ib_pd *ibpd,
>>>> + enum ib_uverbs_advise_mr_advice advice,
>>>> + u32 pf_flags, struct ib_sge *sg_list,
>>>> + u32 num_sge)
>>>> +{
>>>> + struct rxe_pd *pd = container_of(ibpd, struct rxe_pd, ibpd);
>>>> + unsigned int i;
>>>> + int ret = 0;
>>>> +
>>>> + for (i = 0; i < num_sge; ++i) {
>>>> + struct rxe_mr *mr;
>>>> + struct ib_umem_odp *umem_odp;
>>>> +
>>>> + mr = lookup_mr(pd, IB_ACCESS_LOCAL_WRITE,
>>>> + sg_list[i].lkey, RXE_LOOKUP_LOCAL);
>>>> +
>>>> + if (IS_ERR(mr)) {
>>>> + rxe_dbg_pd(pd, "mr with lkey %x not found\n", sg_list[i].lkey);
>>>> + return PTR_ERR(mr);
>>>> + }
>>>> +
>>>> + if (advice == IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_WRITE &&
>>>> + !mr->umem->writable) {
>>>> + rxe_dbg_mr(mr, "missing write permission\n");
>>>> + rxe_put(mr);
>>>> + return -EPERM;
>>>> + }
>>>> +
>>>> + ret = rxe_odp_do_pagefault_and_lock(mr, sg_list[i].addr,
>>>> + sg_list[i].length, pf_flags);
>>>> + if (ret < 0) {
>>>> + if (sg_list[i].length == 0)
>>>> + continue;
>>>> +
>>>> + rxe_dbg_mr(mr, "failed to prefetch the mr\n");
>>>> + rxe_put(mr);
>>>> + return ret;
>>>> + }
>>>> +
>>>> + umem_odp = to_ib_umem_odp(mr->umem);
>>>> + mutex_unlock(&umem_odp->umem_mutex);
>>>> +
>>>> + rxe_put(mr);
>>>> + }
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> +static int rxe_ib_advise_mr_prefetch(struct ib_pd *ibpd,
>>>> + enum ib_uverbs_advise_mr_advice advice,
>>>> + u32 flags, struct ib_sge *sg_list, u32 num_sge)
>>>> +{
>>>> + u32 pf_flags = RXE_PAGEFAULT_DEFAULT;
>>>> +
>>>> + if (advice == IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH)
>>>> + pf_flags |= RXE_PAGEFAULT_RDONLY;
>>>> +
>>>> + if (advice == IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_NO_FAULT)
>>>> + pf_flags |= RXE_PAGEFAULT_SNAPSHOT;
>>>> +
>>>> + /* Synchronous call */
>>>> + if (flags & IB_UVERBS_ADVISE_MR_FLAG_FLUSH)
>>>> + return rxe_ib_prefetch_sg_list(ibpd, advice, pf_flags, sg_list,
>>>> + num_sge);
>>>> +
>>>> + /* Asynchronous call is "best-effort" */
>>>
>>> Asynchronous call is not implemented now, why does this comment appear?
>>
>> Even without the 2nd patch, async calls are reported as successful.
>
>
> Async call is not implemented. How to call "async calls are reported as successful"?
Please see the manual.
cf. https://manpages.debian.org/testing/libibverbs-dev/ibv_advise_mr.3.en.html
If IBV_ADVISE_MR_FLAG_FLUSH is not given to 'flags' parameter,
then this function 'rxe_ib_advise_mr_prefetch()' simply returns 0.
Consequently, ibv_advise_mr(3) and underlying ioctl(2) get no error.
This behaviour is allowd in the spec as I quoted in the last reply.
It might be nice to return -EOPNOTSUPP just below the comment instead,
but not doing so is acceptable according to the spec. Additionally,
such change will be overwritten in the next patch after all.
Thanks,
Daisuke
>
>
> Zhu Yanjun
>
>> The comment is inserted to show the reason, which is based on the
>> description from 'man 3 ibv_advise_mr' as follows:
>> ===
>> An application may pre-fetch any address range within an ODP MR when using the IBV_ADVISE_MR_ADVICE_PREFETCH or IBV_ADVISE_MR_ADVICE_PREFETCH_WRITE advice. Semantically, this operation is best-effort. That means the kernel does not guarantee that underlying pages are updated in the HCA or the pre-fetched pages would remain resident.
>> ===
>>
>> Thanks,
>> Daisuke
>>
>>>
>>> Zhu Yanjun
>>>
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> +int rxe_ib_advise_mr(struct ib_pd *ibpd,
>>>> + enum ib_uverbs_advise_mr_advice advice,
>>>> + u32 flags,
>>>> + struct ib_sge *sg_list,
>>>> + u32 num_sge,
>>>> + struct uverbs_attr_bundle *attrs)
>>>> +{
>>>> + if (advice != IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH &&
>>>> + advice != IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_WRITE &&
>>>> + advice != IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH_NO_FAULT)
>>>> + return -EOPNOTSUPP;
>>>> +
>>>> + return rxe_ib_advise_mr_prefetch(ibpd, advice, flags,
>>>> + sg_list, num_sge);
>>>> +}
>>>
>>
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